Thermally conductive material and thermally conductive sheet molded from the thermally conductive material

ABSTRACT

Disclosed is a thermally conductive material having excellent heat conductivity and insulating properties and having flame retardancy while retaining flexibility and toughness. More specifically, there is provided a thermally conductive material comprising: a hydrogenated copolymer (1) and/or a modified hydrogenated copolymer (2) in which each has a specific structure and is contained in a specific amount; and zinc oxide (3) comprising a core part and acicular crystal parts extending from the core part in four axial directions. The thermally conductive material optionally further comprises a paraffin oil (4), a flame retardant (5), or a filler (6) having a thermal conductivity of 10 to 400 W/m·K (the zinc oxide (3) is excluded).

TECHNICAL FIELD

The present invention relates to a thermally conductive material and athermally conductive sheet molded from the thermally conductive materialwhich are used in applications where the thermally conductive materialand sheet are allowed to adhere closely to semiconductor elements suchas ICs, CPUs, LEDs, or LSIs on electronic substrates in electric andelectronic devices to dissipate heat from the semiconductor elements.

BACKGROUND ART

As digital household appliances have become common, there is anincreasing need for higher-speed and higher-performance electric andelectronic devices. In electric and electronic devices, semiconductorelements for electronic control such as LSIs and CPUs consume more powerand thus produce more heat because of higher integration andhigher-speed operations in computers. Heat needs to be dissipated fromsuch semiconductor elements to prevent problems such as the occurrenceof failures in the semiconductor elements. A method of dissipating heatfor general electric and electronic devices is to install a cooling partsuch as a heatsink in the devices and forcibly cool the heatsink byusing a cooling fan or the like. In compact electric devices such aslaptop computers and densely-packed electronic devices, heat isdissipated by means of application of silicone grease because oflimitations such as the small space available for the installation of acooling fan or the like. However, silicone grease have problems such aslow work efficiency, part contamination due to the squeezing-out of thegrease after application, and limited use under high load due to poorcushioning.

Thermally conductive sheets are used to meet the requirements forhigher-performance electric and electronic devices. A thermallyconductive sheet is a flexible sheet which is effective in placing itbetween a rigid cooling part such as a heatsink and a flexible heatingelement and improving the proximity of both parts. If both parts arebrought closer to each other, heat can be conducted to the cooling partmore efficiently.

The most commonly used thermally conductive sheet is a thermallyconductive sheet produced by mixing a filler having a relatively highthermal conductivity into a silicone rubber. This silicone rubber-basedthermally conductive sheet is easy to handle. However, the siliconerubber-based thermally conductive sheet has problems such as expensivesilicone resin itself as a raw material and an increased number of stepsdue to a required curing step. In addition, a silicone resin containslow molecular weight siloxane in it, so when this thermally conductivesheet is placed on a heating element for use, low molecular weightsiloxane gas is generated. The gas may adhere to an electrode contact orthe like to generate silicon dioxide, leading to contact failure.

In addition, a thermally conductive sheet is also required to meetvarious physical characteristics other than thermal conductivity.

For example, a thermally conductive sheet is required to be electricallyinsulating to prevent failure due to the passage of current through anelectronic substrate. This is because the sheet is often placed on theelectronic substrate with the sheet in contact with the electronicsubstrate.

In addition, if there is a gap between a heating element such as a CPUand a cooling part such as a heatsink, sometimes a thermally conductivesheet having a thickness of greater than 1 mm and 3 cm or less is used.In this case, the thermally conductive sheet is required to be flexibleand tough. This requirement is intended to prevent material breakingwhen the sheet is fixed with the thermally conductive sheet underpressure between the heating element and the cooling part.

In addition, when a thermally conductive sheet having a thickness of 1mm or less is placed on, for example, a CPU on an electronic substrate,sometimes sheet positioning fails on the first try and is separated toplace it again. In this case, if the sheet has poor toughness, the sheetitself is torn off, resulting in poor yield.

In addition, thermally conductive sheets are used not only in electricand electronic devices but also for house floor heating. This latter useis intended to conduct heat from hot water flowing through circulationpipes to the floor. A thin aluminum film is used as a thermallyconductive sheet at present. However, the aluminum film lackscushioning, so it provides poor proximity of the pipes and the floor andcannot heat the whole floor efficiently and uniformly.

Furthermore, if a thermally conductive sheet is used for internal partsof low power electric and electronic devices, the sheet is required tobe flame-retardant in view of safety.

Patent Documents 1 and 2 proposes that a zinc oxide whisker is added toa resin. This addition is intended to make the resin compositionelectrically conductive or make the resin mechanically stronger.

Patent Document 3 proposes that a filler is added to a styrene-basedhydrogenated copolymer produced by hydrogenating a copolymer comprisinga conjugated diene and a vinyl aromatic. This addition is intended tomake the resin composition more resistant to wear and abrasion andmechanically stronger. Although this patent document describes aspherical zinc oxide as a filler, the use of the spherical zinc oxidedoes not allow excellent thermal conductivity to develop. In addition,the patent document has no description of flame retardancy.

Patent Document 4 proposes a resin composition produced by mixing aparaffin oil, a thermally conductive filler, and a flame retardant intoa mixture of a styrene-based thermoplastic elastomer and apropylene-based polymer. The resin composition uses the propylene-basedpolymer for higher processability and heat resistance and the paraffinoil for use of a large amount of the filler and flexibility. Thestyrene-based thermoplastic elastomer and the propylene-based polymerare incompatible with each other regardless of whether or not theparaffin oil is added. For this reason, disadvantages of the resincomposition are poor toughness as a material and brittleness occurringwhen it is processed into a sheet or a molded body. In addition, theamount of the paraffin oil is very large because it is 3.5 times or morethe total amount of styrene-based thermoplastic elastomer andpropylene-based polymer, so the paraffin oil easily bleed out of theinterface between both phases of the incompatible styrene-basedthermoplastic elastomer and propylene-based polymer. For example, when athermally conductive sheet comprising the composition is placed on aCPU, the operation of the CPU allows the thermally conductive sheet tobe exposed to a cooling-heating cycle and this exposure makes theparaffin oil bleed out, leading to contamination of the electronicsubstrate including the CPU. In addition, the use of the propylenepolymer which is a rigid component allows the sheet to lack flexibility.This provides poor proximity of the sheet to the CPU or heatsink andcannot allow the thermal conductivity the sheet originally has todevelop effectively. As a result, the heat dissipation of the sheet ispoor.

Patent Document 5 proposes that a filler such as alumina (aluminumoxide) is added to a styrene-based thermoplastic elastomer. Thisaddition is intended to improve the thermal conductivity of the resincomposition. However, the patent document does not describe use of zincoxide as a filler to give the composition thermal conductivity, apreferred shape of the filler, or chips generated during production ofthe composition. Use of alumina having an amorphous or spherical shape,both of which are common alumina structures, provides the occurrence ofchips due to alumina removal during strand or sheet cutting and thisoccurrence results in poor electrical insulation, causing failure of anelectronic substrate.

Patent Document 6 proposes a product molded from a thermally conductiveresin produced by mixing graphite into a thermoplastic resin. Simplymixing a large amount of graphite increases thermal conductivity greatlybut reduces electrical insulation. For this reason, when the moldedproduct is in contact with an electronic substrate, energization createsa short circuit, causing breakage of a semiconductor element. Inaddition, the product is not preferable because it is a material lackingthe flexibility and toughness which a thermally conductive sheet isrequired to have. In contrast, mixing a small amount of graphite allowsthe product to maintain electrical insulation but have poor thermalconductivity. For this reason, the product is not sufficient as athermally conductive material for semiconductor elements which haverecently produced more heat.

Patent Document 7 discloses a molded product made from a thermallyconductive material comprising a thermoplastic resin and a zinc oxidewhisker. However, the patent document does not describe use of aflexible material and a paraffin oil, so the product is a materiallacking flexibility and toughness. This lack provides poor proximity ofthe product to a cooling part and a heating element and cannot allow thethermal conductivity of the product to develop effectively, so theproduct is not suitable as a thermally conductive sheet.

-   Patent Document 1: Japanese Patent Laid-Open No. 1-225663-   Patent Document 2: Japanese Patent Publication No. 7-51646-   Patent Document 3: Japanese Patent Laid-Open No. 2003-277560-   Patent Document 4: Japanese Patent Laid-Open No. 2003-49046-   Patent Document 5: Japanese Patent Laid-Open No. 2002-206030-   Patent Document 6: Japanese Patent Laid-Open No. 62-131033-   Patent Document 7: Japanese Patent Laid-Open No. 2006-57064

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been made to solve the problems of thermallyconductive materials above and an object thereof is to provide athermally conductive material and a thermally conductive sheet moldedtherefrom characterized by having excellent thermal conductivity andelectrical insulation as well as having flexibility and toughness.

Means for Solving the Problems

The present inventors have conducted intensive studies to solve theproblems and found that a thermally conductive material comprising ahydrogenated copolymer having a specific structure and/or a modifiedhydrogenated copolymer having a specific structure and a zinc oxidecomprising a core part and acicular crystal parts extended from the corepart in four axial directions at a specific ratio and optionally furthercontaining a paraffin oil, a flame retardant, or a filler having athermal conductivity of from 10 to 400 W/m·K has excellent thermalconductivity and electrical insulation while retaining flexibility andtoughness. The inventors have also found that a thermally conductivesheet molded from the thermally conductive material has excellentphysical characteristics which the thermally conductive sheet isrequired to have. These findings have led the inventors to complete theinvention.

More specifically, the present invention is:

[1]

a thermally conductive material comprising:

a hydrogenated copolymer (1) satisfying the following conditions (a) to(d) which is produced by hydrogenating a copolymer of a conjugated dieneand a vinyl aromatic; and/or a modified hydrogenated copolymer (2)having at least one functional group and satisfying the followingconditions (a) to (d), which is produced by hydrogenating a copolymer ofa conjugated diene and a vinyl aromatic; and

a zinc oxide (3) comprising a core part and acicular crystal partsextending from the core in four different axial directions,

wherein the thermally conductive material does not comprise a paraffinoil (4) or a flame retardant (5), and satisfies the following conditions(A) and (B):

(a) a content of a vinyl aromatic unit is greater than 45 mass % and 90mass % or less,

(b) a content of a polymer block comprising the vinyl aromatic is 40mass % or less,

(c) a weight-average molecular weight is 5×10⁴ to 100×10⁴, and

(d) a degree of hydrogenation of double bonds based on the conjugateddiene is 10% or more, and

based on 100 mass % of the thermally conductive material,

(A) a total content of the hydrogenated copolymer (1) and the modifiedhydrogenated copolymer (2), [(1)+(2)], is 10 mass % or more and 90 mass% or less, and

(B) a total content of the zinc oxide (3) having the core part and theacicular crystal parts extending from the core part in four differentaxial directions is 10 mass % or more and 90 mass % or less.

[2]

a thermally conductive material comprising:

a hydrogenated copolymer (1) satisfying the following conditions (a) to(d) which is produced by hydrogenating a copolymer of a conjugated dieneand a vinyl aromatic; and/or a modified hydrogenated copolymer (2)having at least one functional group and satisfying the followingconditions (a) to (d), which is produced by hydrogenating a copolymer ofa conjugated diene and a vinyl aromatic;

a zinc oxide (3) comprising a core part and acicular crystal partsextending from the core in four different axial directions; and

a paraffin oil (4),

wherein the thermally conductive material does not comprise a flameretardant (5), and satisfies the following conditions (A) to (C):

(a) a content of a vinyl aromatic unit is greater than 45 mass % and 90mass % or less,

(b) a content of a polymer block comprising the vinyl aromatic is 40mass % or less,

(c) a weight-average molecular weight is 5×10⁴ to 100×10⁴, and

(d) a degree of hydrogenation of double bonds based on the conjugateddiene is 10% or more, and

based on 100 mass % of the thermally conductive material,

(A) a total content of the hydrogenated copolymer (1), the modifiedhydrogenated copolymer (2), and the paraffin oil (4), [(1)+(2)+(4)], is10 mass % or more and 90 mass % or less,

(B) a content of the zinc oxide (3) is 10 mass % or more and 90 mass %or less, and

(C) a ratio of a mass of the paraffin oil (4) to a total mass of thehydrogenated copolymer (1) and the modified hydrogenated copolymer (2),[(4)/{(1)+(2)}], is greater than 0 and 2 or less.

[3]

a thermally conductive material comprising:

a hydrogenated copolymer (1) satisfying the following conditions (a) to(d) which is produced by hydrogenating a copolymer of a conjugated dieneand a vinyl aromatic; and/or a modified hydrogenated copolymer (2)having at least one functional group and satisfying the followingconditions (a) to (d), which is produced by hydrogenating a copolymer ofa conjugated diene and a vinyl aromatic;

a zinc oxide (3) comprising a core part and acicular crystal partsextending from the core in four different axial directions;

a paraffin oil (4); and

a flame retardant (5),

wherein the thermally conductive material satisfies the followingconditions (A) to (E):

(a) a content of a vinyl aromatic unit is greater than 45 mass % to 90mass % or less,

(b) a content of a polymer block comprising the vinyl aromatic is 40mass % or less,

(c) a weight-average molecular weight is 5×10⁴ to 100×10⁴, and

(d) a degree of hydrogenation of double bonds based on the conjugateddiene is 10% or more, and

based on 100 mass % of the thermally conductive material,

(A) a total content of the hydrogenated copolymer (1), the modifiedhydrogenated copolymer (2), and the paraffin oil (4), [(1)+(2)+(4)], is10 mass % or more and 87 mass % or less,

(B) a content of the zinc oxide (3) is 10 mass % or more and 87 mass %or less,

(C) a ratio of a mass of the paraffin oil (4) to a total mass of thehydrogenated copolymer (1) and the modified hydrogenated copolymer (2),[(4)/{(1)+(2)}], is greater than 0 and 2 or less,

(D) a content of the flame retardant (5) is 3 mass % or more and 30 mass% or less, and

(E) a ratio of a mass of the flame retardant (5) to a total mass of thehydrogenated copolymer (1), the modified hydrogenated copolymer (2), andthe paraffin oil (4), [(5)/{(1)+(2)+(4)}], is 0.2 or more and 3 or less.

[4]

a thermally conductive material comprising:

a hydrogenated copolymer (1) satisfying the following conditions (a) to(d) which is produced by hydrogenating a copolymer of a conjugated dieneand a vinyl aromatic; and/or a modified hydrogenated copolymer (2)having at least one functional group and satisfying the followingconditions (a) to (d), which is produced by hydrogenating a copolymer ofa conjugated diene and a vinyl aromatic;

a zinc oxide (3) comprising a core part and acicular crystal partsextending from the core in four different axial directions;

a paraffin oil (4);

a flame retardant (5); and

a filler having a thermal conductivity of 10 to 400 W/m·K (6) (excludingthe zinc oxide (3)),

wherein the thermally conductive material satisfies the followingconditions (A) to (F):

(a) a content of a vinyl aromatic unit is greater than 45 mass % and 90mass % or less,

(b) a content of a polymer block comprising the vinyl aromatic is 40mass % or less,

(c) a weight-average molecular weight is 5×10⁴ to 100×10⁴, and

(d) a degree of hydrogenation of double bonds based on the conjugateddiene is 10% or more, and

based on 100 mass % of the thermally conductive material,

(A) a total content of the hydrogenated copolymer (1), the modifiedhydrogenated copolymer (2), and the paraffin oil (4), [(1)+(2)+(4)], is10 mass % or more and 87 mass % or less,

(B) a total content of the zinc oxide (3) and the filler (6), [(3)+(6)],is 10 mass % or more and 87 mass % or less,

(C) a ratio of a mass of the paraffin oil (4) to a total mass of thehydrogenated copolymer (1) and the modified hydrogenated copolymer (2),[(4)/{(1)+(2)}], is greater than 0 and 2 or less,

(D) a content of the flame retardant (5) is 3 mass % or more and 30 mass% or less,

(E) a ratio of a mass of the flame retardant (5) to a total mass of thehydrogenated copolymer (1), the modified hydrogenated copolymer (2), andthe paraffin oil (4), [(5)/{(1)+(2)+(4)}], is 0.2 or more and 3 or less,and

(F) a ratio of a mass of the filler (6) to a total mass [(3)+(6)] of thezinc oxide (3) and the filler (6) is greater than 0 and less than 0.5.

[5]

the thermally conductive material according to any one of items [1] to[4], wherein the modified hydrogenated copolymer (2) has at least onefunctional group selected from a hydroxy group, an epoxy group, an aminogroup, a silanol group, and an alkoxysilane group.

[6]

the thermally conductive material according to any one of items [1] to[5], wherein the content of the vinyl aromatic polymer block in thehydrogenated copolymer (1) and/or the modified hydrogenated copolymer(2) is 10 to mass %.

[7]

the thermally conductive material according to any one of items [1] to[5], wherein the content of the vinyl aromatic polymer block in thehydrogenated copolymer (1) and/or the modified hydrogenated copolymer(2) is less than 10 mass %.

[8]

the thermally conductive material according to any one of items [1] to[7], wherein the hydrogenated copolymer (1) and/or the modifiedhydrogenated copolymer (2) has at least one structure selected from thefollowing general formulas:B;  (i)B-A;  (ii)B-A-B;  (iii)(B-A)_(m)-Z; and  (iv)(B-A)_(n)-Z-A_(p),  (v)(wherein B represents a random copolymer block of the conjugated dieneand the vinyl aromatic, and A represents the vinyl aromatic polymerblock. m is an integer of 2 or more, and each of n and p is an integerof 1 or more. Z represents a coupling agent residue.)[9]

the thermally conductive material according to any one of items [1] to[8], wherein the modified hydrogenated copolymer (2) has at least onefunctional group selected from the following formulas (a) to (n):

(wherein R1 to R4 independently represent hydrogen or a hydrocarbongroup having a carbon number of 1 to 24, or a hydrocarbon group having acarbon number of 1 to 24 which has a functional group selected from ahydroxy group, an epoxy group, an amino group, a silanol group, and analkoxysilane group. R5 represents a hydrocarbon chain having a carbonnumber of 1 to 48 or a hydrocarbon chain having a carbon number of 1 to48 which has a functional group selected from a hydroxy group, an epoxygroup, an amino group, a silanol group, and an alkoxysilane group.Elements such as oxygen, nitrogen, and silicon may bind to thehydrocarbon groups of R1 to R4 and the hydrocarbon chain of R5 in whicha binding way that such elements do not take a form of a hydroxy group,an epoxy group, a silanol group, or an alkoxysilane group. R6 representshydrogen or an alkyl group having a carbon number of 1 to 8.)[10]

the thermally conductive material according to any one of items [1] to[9], wherein the modified hydrogenated copolymer (2) is obtained byallowing addition reaction to take place between a modifier containing afunctional group and a living end of an unhydrogenated copolymerobtained with an organolithium compound as a polymerization catalyst andthen hydrogenating the modified unhydrogenated copolymer (2) obtained.

[11]

the thermally conductive material according to any one of items [3] to[10], wherein a phosphorus-based flame retardant is contained as theflame retardant (5).

[12]

the thermally conductive material according to item [11], wherein thephosphorus-based flame retardant is phosphazene.

[13]

the thermally conductive material according to any one of items [4] to[12], wherein the filler (6) comprises at least one selected fromsilicon nitride, aluminum nitride, silicon carbide, boron nitride, andgraphite.

[14]

the thermally conductive material according to any one of items [4] to[12], wherein the filler (6) comprises at least one selected fromaluminum nitride and boron nitride.

[15]

the thermally conductive material according to any one of items [1],[2], and [5] to [14], wherein the content of the zinc oxide (3) is 65mass % or more and 90 mass % or less based on 100 mass % of thethermally conductive material.

[16]

the thermally conductive material according to any one of items [3] to[14], wherein the thermally conductive material comprises a flameretardant (5) and the content of the zinc oxide (3) is 65 mass % or moreand 87 mass % or less based on 100 mass % of the thermally conductivematerial.

[17]

a thermally conductive sheet having a thickness of 30 μm to 1 mm, whichis obtained by molding from the thermally conductive material accordingto any one of items [1] to [16]

[18]

a thermally conductive sheet having a thickness of greater than 1 mm to3 cm or less, which is obtained by molding from a thermally conductivematerial according to any one of items [1] to [16].

Advantages of the Invention

The present invention can provide a thermally conductive material and athermally conductive sheet molded therefrom that are both characterizedby having excellent thermal conductivity and electrical insulation aswell as having flexibility and toughness.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention requires use of a hydrogenated copolymer (1)having a specific structure and/or a modified hydrogenated copolymer (2)having a specific structure and a zinc oxide (3) comprising a core partand acicular crystal parts extending from the core part in fourdifferent axial directions at a specific ratio. If the hydrogenatedcopolymer (1) having a specific structure and/or the modifiedhydrogenated copolymer (2) having a specific structure is contained at aspecific ratio, the zinc oxide (3) comprising the core part and theacicular crystal parts extending from the core part in four differentaxial directions can be mixed in large amounts, providing the thermallyconductive material and the thermally conductive sheet molded therefromthat both have excellent thermal conductivity. In addition, if the zincoxide (3) comprising the core part and the acicular crystal partsextending from the core part in four different axial directions is used,the thermally conductive material and the thermally conductive sheetmolded therefrom that both have excellent thermal conductivity can beobtained.

Moreover, if a paraffin oil (4) is contained at a specific ratio, theflexibility, thermal conductivity, and fabricability can be improved. Inaddition, if a flame retardant (5) is contained at a specific ratio,flame retardancy can be provided while other physical characteristicsare almost entirely maintained. Furthermore, if a filler (6) (excludingthe zinc oxide (3)) having a thermal conductivity of 10 to 400 W/m·K iscontained at a specific ratio, a higher thermal conductivity can beprovided.

The hydrogenated copolymer (1) and/or the modified hydrogenatedcopolymer (2) are produced by hydrogenating a copolymer of a conjugateddiene and a vinyl aromatic. Hereinafter, a copolymer of a conjugateddiene and a vinyl aromatic that can be hydrogenated into a hydrogenatedcopolymer (1) is referred to as an unhydrogenated copolymer (1); acopolymer of a conjugated diene and a vinyl aromatic that can behydrogenated into a modified hydrogenated copolymer (2) is referred toas an a modified unhydrogenated copolymer (2); and a unhydrogenatedcopolymer (1) and a modified unhydrogenated copolymer (2) iscollectively referred to as unhydrogenated copolymers.

A conjugated diene refers to a diolefin having a pair of conjugateddouble bonds. Examples thereof may include 1,3-butadiene,2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, and the like,especially common conjugated dienes may include 1,3-butadiene,2-methyl-1,3-butadiene (isoprene). These compounds may be used alone orin combination of two or more of them.

In addition, examples of the vinyl aromatic may include styrene,α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene,N,N-dimethyl-p-aminoethylstyrene, N,N-diethyl-p-aminoethylstyrene andthe like. These compounds may be used alone or in combination of two ormore of them.

A content of the vinyl aromatic unit in each of the hydrogenatedcopolymer (1) and the modified hydrogenated copolymer (2) is greaterthan 45 mass % and 90 mass % or less, preferably greater than 45 mass %and 88 mass % or less, and more preferably greater than 45 mass % and 86mass % or less. Any content in the above range can provide the thermallyconductive material according to the present invention having excellentflexibility and toughness.

The content of the vinyl aromatic unit can be determined with anultraviolet spectrophotometer, an infrared spectrophotometer, a nuclearmagnetic resonance (NMR) apparatus, or the like.

The content of the polymer block comprising the vinyl aromatic in eachof the hydrogenated copolymer (1) and the modified hydrogenatedcopolymer (2) is 40 mass % or less. In this case, the hydrogenatedcopolymer (1) and the modified hydrogenated copolymer (2) have goodflexibility and blocking resistance.

If a hydrogenated copolymer (1) and a modified hydrogenated copolymer(2) having excellent blocking resistance are to be obtained, the contentof the polymer block comprising the vinyl aromatic is preferably 10 to40 mass %, more preferably 13 to 37 mass %, and much more preferably 15to 35 mass %.

If a hydrogenated copolymer (1) and a modified hydrogenated copolymer(2) having excellent flexibility are to be obtained, the content of thepolymer block comprising the vinyl aromatic is preferably less than 10mass %, more preferably less than 8 mass %, and much more preferablyless than 5 mass %.

The content of the polymer block comprising the vinyl aromatic can bedetermined as follows. The weight of a polymer block componentcomprising the vinyl aromatic (excluding a vinyl aromatic polymercomponent having an average degree of polymerization of about 30 orless) as determined, for example, by a method which oxidizes anddegrades an unhydrogenated copolymer by tert-butylhydroperoxide withosmium tetraoxide as a catalyst (which is the method described in I. M.KOLTHOFF, et al., J. Polym. Sci. 1, 429(1946)) can be used to calculatethe content from the following equation.

Content of the polymer block comprising the vinyl aromatic (mass%)={(mass of the polymer block comprising the vinyl aromatic in anunhydrogenated copolymer (1) and/or a modified unhydrogenated copolymer(2))/(mass of the unhydrogenated copolymer (1) and/or the modifiedunhydrogenated copolymer (2))}×100

Note that the block content of the vinyl aromatic in each of thehydrogenated copolymer (1) and the modified hydrogenated copolymer (2)is preferably less than 40 mass %, more preferably 20 mass % or less,and much more preferably 18 mass % or less. As used herein, the term“block content” refers to a ratio of the amount of the vinyl aromaticpolymer block to the total amount of the vinyl aromatic in thehydrogenated copolymer (1) or the modified hydrogenated copolymer (2).To obtain a composition having good flexibility, it is recommended thatthe block content be in the above range.

In addition to the polymer block comprising the vinyl aromatic, thehydrogenated copolymer (1) and the modified hydrogenated copolymer (2)each contain 5 mass % or more of a vinyl aromatic unit. If the contentof the vinyl aromatic unit other than the polymer block comprising avinyl aromatic is 5 mass % or more, such content is effective inimproving the heat resistance of the hydrogenated copolymer (1) and themodified hydrogenated copolymer (2). Moreover, such content can inhibitthe crystallization of parts other than the polymer block comprising thevinyl aromatic, providing good flexibility. Furthermore, such contentallows a zinc oxide (3) and a filler (6) to be added in large amounts,providing good thermal conductivity.

The weight-average molecular weight of each of the hydrogenatedcopolymer (1) and the modified hydrogenated copolymer (2) is 5×10⁴ to100×10⁴, preferably 10×10⁴ to 80×10⁴, and more preferably 13×10⁴ to50×10⁴. If a hydrogenated copolymer (1) and a modified hydrogenatedcopolymer (2) having a content of the polymer block comprising the vinylaromatic of 10 to 40 mass % is used, it is recommended that theweight-average molecular weight of each of them be greater than 10×10⁴and less than 50×10⁴, preferably 13×10⁴ to 40×10⁴, and more preferably15×10⁴ to 30×10⁴. A weight-average molecular weight of 5×10⁴ or moreprovides good toughness and a weight-average molecular weight of 100×10⁴or less provides good flexibility, so the weight-average molecularweight in this range is preferable. Moreover, the weight-averagemolecular weight of 5×10⁴ to 100×10⁴ provides a low content of thevolatile component because of a low content of the low-molecular-weightcomponent. It is recommended that the molecular weight distribution(Mw/Mn) (ratio of weight-average molecular weight (Mw) to number-averagemolecular weight (Mn)) of each of the hydrogenated copolymer (1) and themodified hydrogenated copolymer (2) be preferably 1.01 to 8.0, morepreferably 1.1 to 6.0, and much more preferably 1.1 to 5.0, in view offabricability. The shape of the molecular weight distribution determinedby gel permeation chromatography (GPC) is not particularly limited. Thecopolymers may have a polymodal molecular weight distribution where twoor more peaks are present, but they preferably have a monomodalmolecular weight distribution where a single peak is present.

The molecular weight of each of the hydrogenated copolymer (1) and themodified hydrogenated copolymer (2), which is the molecular weightcorresponding to the peak on the chromatogram obtained from measurementby gel permeation chromatography (GPC), is the weight-average molecularweight determined by using a calibration curve created from themeasurement of a commercially available standard polystyrene (preparedby using the peak molecular weight of the standard polystyrene). Themolecular weight distributions of the hydrogenated copolymer (1) and themodified hydrogenated copolymer (2) can also be obtained in the same wayfrom GPC measurement.

For the hydrogenated copolymer (1) and modified hydrogenated copolymer(2), the degree of hydrogenation of double bonds based on the conjugateddiene in the respective unhydrogenated copolymers is 10% or more,preferably 75% or more, and much more preferably 85% or more. A degreeof hydrogenation of 10% or more provides a good heat resistance withoutdecreases in flexibility, strength, and elongation due to thermaldegradation. If a thermally conductive material having excellent heatresistance is to be obtained, it is recommended that the degree ofhydrogenation be preferably 85% or more, more preferably 90% or more,and much more preferably 95% or more. If a thermally conductive materialhaving excellent weather resistance is to be obtained, it is recommendedthat the degree of hydrogenation be preferably 75% or more, morepreferably 85% or more, and much preferably 90% or more. In addition, ifcrosslinking is necessary, it is recommended that the degree ofhydrogenation be preferably 98% or less, more preferably 95% or less,and much more preferably 90% or less.

As used herein, the degree of hydrogenation of double bonds based on theconjugated diene refers to a ratio of the hydrogenated double bonds ofeach of the hydrogenated copolymer (1) and the modified hydrogenatedcopolymer (2) to the double bonds of the conjugated diene that each ofthe unhydrogenated copolymer (1) and the modified unhydrogenatedcopolymer (2) contains.

The degrees of hydrogenation of the hydrogenated copolymer (1) and themodified hydrogenated copolymer (2) can be determined with an infraredspectrophotometer, a nuclear magnetic resonance (NMR) apparatus, or thelike.

Here, the degree of hydrogenation of the aromatic double bond based onthe vinyl aromatic in a copolymer is not particularly limited, andpreferably 50% or less, more preferably 30% or less, and much morepreferably 20% or less.

The hydrogenated copolymer (1) and the modified hydrogenated copolymer(2) particularly preferably have at least one structure selected fromthe following general formulas (i) to (v). In addition, they may be amixture having more than one structure represented by the followingformulas at any ratio:B;  (i)B-A;  (ii)B-A-B;  (iii)(B-A)_(m)-Z; and  (iv)(B-A)_(n)-Z-A_(p)  (v)(wherein B represents a random copolymer block (hereinafter referred toas block B) of a conjugated diene and a vinyl aromatic, and A representsa vinyl aromatic polymer block (hereinafter referred to as block A). mis an integer of 2 or more, and each of n and p is an integer of 1 ormore. Z represents a coupling agent residue.)

In the general formulas, the vinyl aromatic in block B may bedistributed uniformly or in a tapered form. In addition, block B mayhave multiple parts where the vinyl aromatic is uniformly distributedand/or multiple parts where the vinyl aromatic is distributed in atapered form. m is an integer of 2 or more, and preferably an integer of2 to 10, and each of n and p is an integer of 1 or more, and preferably1 to 10. The crystalline part in a copolymer can be minimized oreliminated by forming a random block B structure of a conjugated dieneand a vinyl aromatic, allowing the zinc oxide (3) and/or the filler (6)to be mixed in large amounts.

The modified hydrogenated copolymer (2) has a functional group in apolymer chain. Examples of the functional group may include functionalgroups selected from a hydroxy group, a carboxy group, a carbonyl group,a thiocarbonyl group, an acid halide group, an acid anhydride group, acarboxylic acid group, a thiocarboxylic acid group, an aldehyde group, atioaldehyde group, a carboxylic ester group, an epoxy group, a thioepoxygroup, a sulfide group, an isocyanate group, an isothiocyanate group, anamide group, a sulfonic acid group, a sulfonic ester group, a phosphategroup, a phosphate group, an amino group, an imino group, a nitrilegroup, a pyridyl group, a quinoline, a silicon halide group, a silanolgroup, an alkoxysilane group, a tin halide group, an alkoxy tin group, aphenyltin group, and the like. The copolymer preferably has at least onefunctional group selected from a hydroxy group, an amino group, an epoxygroup, a silanol group, and an alkoxysilane group, and more preferablyhas at least one functional group selected from a hydroxy group, anamino group, and an epoxy group. In the present invention, the copolymerparticularly preferably has a functional group selected from functionalgroups represented by the following general formulas.

(wherein R1 to R4 independently represent hydrogen or a hydrocarbongroup having a carbon number of 1 to 24, or a hydrocarbon group having acarbon number of 1 to 24 which has a functional group selected from ahydroxy group, an epoxy group, an amino group, a silanol group, and analkoxysilane group. R5 represents a hydrocarbon chain having a carbonnumber of 1 to 48 or a hydrocarbon chain having a carbon number of 1 to48 which has a functional group selected from a hydroxy group, an epoxygroup, an amino group, a silanol group, and an alkoxysilane group. Here,a functional group containing elements such as oxygen, nitrogen, orsilicon may bind to the hydrocarbon groups of R1 to R4 and thehydrocarbon chain of R5 in such a binding way that such an element doesnot take the form of a hydroxy group, an epoxy group, a silanol group,or an alkoxysilane group. R6 represents hydrogen or an alkyl grouphaving a carbon number of 1 to 8.)

The modified hydrogenated copolymer (2) is obtained by reacting amodifier containing such a functional group with the polymerizedcopolymer.

A modified hydrogenated copolymer (2) can be obtained by allowingaddition reaction to take place between the living end of anunhydrogenated copolymer obtained with an organolithium compound as apolymerization catalyst and a modifier containing a functional group andthen hydrogenating the resulting copolymer.

Other methods for obtaining the modified hydrogenated copolymer (2) mayinclude a method in which an organoalkaline metal compound such as anorganolithium compound is reacted with a hydrogenated copolymer (1)(metallation reaction) and then addition reaction is allowed to takeplace between the copolymer to which the organoalkaline metal has beenadded and a modifier containing a functional group.

It is preferable that the hydrogenated copolymer (1) and/or the modifiedhydrogenated copolymer (2) show essentially no crystallization peak inthe temperature range of from −50 to 100° C. when differential scanningcalorimetry (DSC) is used. Herein, the phrase essentially nocrystallization peak in the temperature range of from −50 to 100° C.”refers to no peak appearing because of crystallization in thistemperature range or the amount of heat required for crystallization ata peak being less than 3 J/g even if the peak due to crystallization isfound. A zinc oxide (3) and/or a filler (6) can be mixed in largeamounts by minimizing or eliminating the crystalline part. This isbecause the zinc oxide (3) and/or the filler (6) cannot enter thecrystalline part.

At least one peak of loss tangent (tan δ) in a dynamic viscoelasticspectrum of the hydrogenated copolymer (1) and/or the modifiedhydrogenated copolymer (2) is preferably in a range of from −30 to 80°C., more preferably in a range of from −20 to 70° C., and much morepreferably in a range of from −20 to 50° C. The peaks of tan δ presentin a range of from −30 to 80° C. are due to block B. The presence of atleast one peak of tan δ in the range of from −30 to 80° C. providesexcellent flexibility and toughness.

The microscopic structure (ratio of the cis, trans, and vinyl content)of the conjugated diene part of the unhydrogenated copolymer (1) and themodified unhydrogenated copolymer (2) can be arbitrarily changed by theuse of a polar compound as described later or the like and is notparticularly limited. Generally, if 1,3-butadiene is used as aconjugated diene, the 1,2-vinyl bond content is 5 to 80% and preferably10 to 60%, based on 100% of the conjugated diene part. If isoprene isused as a conjugated diene or if 1,3-butadiene and isoprene are usedtogether, it is recommended that the total content of the 1,2-vinyl bondand the 3,4-vinyl bond be preferably 3 to 75% and more preferably 5 to60%. Here, in the present invention, the total content of the 1,2-vinylbond and the 3,4-vinyl bond (however, the 1,2-vinyl bond content when1,3-butadiene is used as a conjugated diene) is hereinafter referred toas the vinyl bond content.

The vinyl bond content based on the conjugated diene of theunhydrogenated copolymer (1) and the modified unhydrogenated copolymer(2) can be determined with an infrared spectrophotometer (e.g., theHampton technique), a nuclear magnetic resonance (NMR) apparatus, or thelike.

In addition, it is recommended that the difference between the maximumand minimum of the vinyl bond content in molecular chains in theunhydrogenated copolymer (1) and the modified unhydrogenated copolymer(2) be preferably less than 10%, more preferably 8% or less, and muchmore preferably 6% or less. The vinyl bond in the copolymer chains maybe distributed uniformly or in a tapered form. Here, the differencebetween the maximum and minimum of the vinyl bond content refers to adifference between the maximum and minimum of the vinyl bond content asdetermined by polymerization conditions, more specifically the type andamount of a vinyl content adjusting agent and polymerizationtemperature.

The difference between the maximum and minimum of the vinyl bond contentin the conjugated diene polymer chain can be controlled, for example, bypolymerization temperature during the polymerization of the conjugateddiene or during the copolymerization of the conjugated diene and thevinyl aromatic. If the type and amount of a vinyl content adjustingagent such as a tertiary amine compound or an ether compound areconstant, the content of vinyl bonds incorporated in polymer chainsbeing polymerized is determined by polymerization temperature.Therefore, an isothermally polymerized polymer is a polymer in which thevinyl bonds are uniformly dispersed. In contrast, a polymer polymerizedat elevated temperature is a polymer having a difference in the vinylbond content in molecular chains, for example, initially (lowtemperature polymerization) a high vinyl bond content and later (hightemperature polymerization) a low vinyl bond content. By hydrogenating acopolymer having such a structure, a hydrogenated copolymer (1) and amodified hydrogenated copolymer (2) having a difference in the vinylbond content in molecular chains are obtained.

In the present invention, an unhydrogenated copolymer is obtained, forexample, by anionic living polymerization in a hydrocarbon solvent usingan initiator such as an organoalkaline metal compound. Examples of thehydrocarbon solvent may include aliphatic hydrocarbons such as n-butane,isobutane, n-pentane, n-hexane, n-heptane, and n-octane, alicyclichydrocarbons such as cyclohexane, cycloheptane, and methylcycloheptane,and aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene.

In addition, examples of the initiator may include aliphatic hydrocarbonalkali metal compounds, aromatic hydrocarbon alkali metal compounds, andorganic amino alkali metal compounds that are all known to have anionicpolymerization activity for a conjugated diene and a vinyl aromatic.Examples of an alkali metal contained in the initiator may includelithium, sodium, and potassium. Preferable organoalkaline metalcompounds are aliphatic and aromatic hydrocarbon lithium compoundshaving a carbon number of 1 to 20 and may include compounds containingone lithium atom per a molecule, and dilithium compounds, trilithiumcompounds, and tetralithium compounds containing two or more lithiumatoms per a molecule.

Examples of the preferable organoalkaline metal compounds may includen-propyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium,n-pentyllithium, n-hexyllithium, benzillithium, phenyllithium,tolyllithium, a reaction product of diisopropenylbenzene andsec-butyllithium, and a reaction product of divinylbenzene,sec-butyllithium, and a small amount of 1,3-butadiene. A lithiumcompound disclosed in U.S. Pat. No. 5,708,092 in which1-(t-butoxy)propyllithium and an isoprene monomer of one or a fewmolecules for improved solubility of the lithium compound are inserted;siloxy group-containing alkyllithium such as1-(t-butyldimethylsiloxy)hexyllithium disclosed in British Patent No.2,241,239; and aminolithiums such as amino group-containingalkyllithium, lithium diisopropylamide, and lithium hexamethyldisilazidedisclosed in U.S. Pat. No. 5,527,753 can also be used.

In the present invention, when a conjugated diene and a vinyl aromaticare copolymerized with an organoalkaline metal compound as anpolymerization initiator, a tertiary amine compound or an ether compoundcan be added as an adjusting agent to adjust the content of the vinylbonds (1,2-bond or 3,4-bond) derived from the conjugated diene to beincorporated in the polymer and the random copolymerization of theconjugated diene and the vinyl aromatic.

The tertiary amine compound is a compound represented by the generalformula R₁R₂R₃N (wherein R₁, R₂, and R₃ independently represent ahydrocarbon group having a carbon number of 1 to 20 or a hydrocarbongroup having a tertiary amino group.). Examples thereof may includetrimethylamine, triethylamine, tributylamine, N,N-dimethylaniline,N-ethylpiperidine, N-methylpyrrolidine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetraethylethylenediamine, 1,2-dipiperidinoethane,trimethylaminoethylpiperazine, andN,N,N′,N″,N″-pentamethylethylenetriamine,N,N′-dioctyl-p-phenylenediamine.

The ether compound is selected from linear-chain ether compounds andcyclic ether compounds.

Examples of the linear-chain ether compounds may include dialkyl ethercompounds of ethylene glycol such as dimethyl ether, diethyl ether,diphenyl ether, ethylene glycol dimethyl ether, ethylene glycol diethylether, and ethylene glycol dibutyl ether; and dialkyl ether compounds ofdiethylene glycol such as diethylene glycol dimethyl ether, diethyleneglycol diethyl ether, and diethylene glycol dibutyl ether.

Examples of the cyclic ether compounds may include tetrahydrofuran,dioxane, 2,5-dimethyloxolane, 2,2,5,5-tetramethyloxolane,2,2-bis(2-oxolanyl)propane, and alkyl ether of furfuryl alcohol.

The method which copolymerizes a conjugated diene and a vinyl aromaticwith an organoalkaline metal compound as a polymerization initiator inthe present invention may be batch polymerization, continuouspolymerization, or a combination thereof. Especially, continuouspolymerization is recommended for adjusting the molecular weightdistribution to an appropriate range. Polymerization temperature isgenerally 0° C. to 180° C., preferably 30° C. to 150° C. The time takenfor polymerization varies depending on the conditions and usually 48hours or less, and more preferably 0.1 to 10 hours. In addition,polymerization is preferably performed in an atmosphere of an inert gassuch as nitrogen gas. Polymerization pressure should be in a range ofpressure that is enough to maintain the monomer and solvent in liquidphase in the polymerization temperature range and is not particularlylimited. Moreover, care should be taken to prevent impurities such aswater, oxygen, and carbon dioxide that may inactivate the catalyst andliving polymer from entering the polymerization system.

On completion of polymerization, coupling reaction can be allowed totake place by adding a required amount of a bifunctional or higherfunctional coupling agent. Any known bifunctional coupling agent can beused and is not particularly limited. Examples thereof may includedihalogen compounds such as dimethyldichlorosilane anddimethyldibromosilane; and acid esters such as methyl benzoate, ethylbenzoate, phenyl benzoate, and phthalate esters.

In addition, any known trifunctional or higher functional polyfunctionalcoupling agent can be used and is not particularly limited. Examplesthereof may include trivalent or higher valent polyalcohols; epoxidizedsoybean oil; polyvalent epoxy compounds such as diglycidyl bisphenol A;halogenated silicon compounds represented by the general formulaR_((4-n))SiX_(n) (wherein R represents a hydrocarbon group having acarbon number of 1 to 20, X represents a halogen, and n is 3 or 4); andhalogenated tin compounds. Examples of the halogenated silicon compoundsmay include methylsilyltrichloride, t-butylsilyltrichloride, silicontetrachloride, and bromides thereof. Examples of the halogenated tincompounds may include methyltintrichloride, t-buthyltintrichloride, andpolyvalent halides such as tin tetrachloride. Dimethyl carbonate,diethyl carbonate and the like can also be used.

In the present invention, a modifier used to obtain a modifiedhydrogenated copolymer (2) having at least one functional group selectedfrom a hydroxy group, an epoxy group, an amino group, a silanol group,and an alkoxysilane group is exemplified by the modifier described inJapanese Patent Publication No. 4-39495 or the following.

According to claim 9, examples of modifiers having functional groupsrepresented by the general formulas (a) to (f) may includetetraglycidyl-m-xylenediamine,tetraglycidyl-1,3-bisaminomethylcyclohexane,tetraglycidyl-p-phenylenediamine, tetraglycidyldiaminodiphenylmethane,diglycidylaniline, diglycidyl-o-toluidine,N-(1,3-dibutylbutylidene)-3-(triethoxysilyl)-1-propaneamine,4-di(β-trimethoxysilylethyl)aminostyrene,4-di(β-triethoxysilylethyl)aminostyrene,4-di(β-triethoxysilylpropyl)aminostyrene, and4-di(γ-triethoxysilylpropyl)aminostyrene;

Examples of a modifier having a functional group represented by theformula (g) may include cyclic lactones such as ε-caprolactone,δ-valerolactone, butyrolactone, γ-caprolactone, and γ-valerolactone;

Examples of a modifier having a functional group represented by theformula (h) may include 4-methoxybenzophenone, 4-ethoxybenzophenone,4,4′-bis(methoxy)benzophenone, 4,4′-bis(ethoxy)benzophenone,γ-glycidoxypropyltripropoxysilane, and γ-glycidoxypropyltributoxysilane;

Examples of modifiers having functional groups represented by theformulas (i) and (j) may include γ-glycidoxyethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-glycidoxybutyltrimethoxysilane,γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltripropoxysilane,γ-glycidoxypropoxytributoxysilane, γ-glycidoxypropyltriphenoxysilane andthe like;

γ-glycidoxypropyl methyl dimethoxysilane,γ-glycidoxypropylethyldimethoxysilane,γ-glycidoxypropylethyldiethoxysilane,γ-glycidoxypropylmethyldiethoxysilane,γ-glycidoxypropylmethyldipropoxysilane,γ-glycidoxypropylmethyldibutoxysilane,γ-glycidoxypropylmethyldiphenoxysilane,γ-glycidoxypropyldimethylmethoxysilane,γ-glycidoxypropyldiethylethoxysilane,γ-glycidoxypropyldimethylethoxysilane,γ-glycidoxypropyldimethylphenoxysilane,γ-glycidoxypropyldiethylmethoxysilane, γ-glycidoxypropylmethyldiisopropenoxysilane, and the like;

bis(γ-glycidoxypropyl)dimethoxysilane,bis(γ-glycidoxypropyl)diethoxysilane,bis(γ-glycidoxypropyl)dipropoxysilane,bis(γ-glycidoxypropyl)dibutoxysilane,bis(γ-glycidoxypropyl)diphenoxysilane,bis(γ-glycidoxypropyl)methylmethoxysilane,bis(γ-glycidoxypropyl)methylethoxysilane,bis(γ-glycidoxypropyl)methylpropoxysilane,bis(γ-glycidoxypropyl)methylbutoxysilane,bis(γ-glycidoxypropyl)methylphenoxysilane, and the like;

tris(γ-glycidoxypropyl)methoxysilane,γ-methacryloxypropyltrimethoxysilane,γ-methacryloxypropyltriethoxysilane,γ-methacryloxymethyltrimethoxysilane,γ-methacryloxyethyltriethoxysilane,bis(γ-methacryloxypropyl)dimethoxysilane,tris(γ-methacryloxypropyl)methoxysilane, and the like;

β-(3,4-epoxycyclohexyl)ethyl-trimethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-triethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-tripropoxysilane,β-(3,4-epoxycyclohexyl)ethyl-tributoxysilane,β-(3,4-epoxycyclohexyl)ethyl-triphenoxysilane,β-(3,4-epoxycyclohexyl)propyl-trimethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-methyldimethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-ethyldimethoxysilane, and the like;

β-(3,4-epoxycyclohexyl)ethyl-ethyldiethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-methyldiethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-methyldipropoxysilane,β-(3,4-epoxycyclohexyl)ethyl-methyldibutoxysilane,β-(3,4-epoxycyclohexyl)ethyl-methyldiphenoxysilane,β-(3,4-epoxycyclohexyl)ethyl-dimethylmethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-diethylethoxysilane, and the like;

β-(3,4-epoxycyclohexyl)ethyl-dimethylethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-dimethylpropoxysilane,β-(3,4-epoxycyclohexyl)ethyl-dimethylbutoxysilane,β-(3,4-epoxycyclohexyl)ethyl-dimethylphenoxysilane,β-(3,4-epoxycyclohexyl)ethyl-diethylmethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-methyldiisopropenoxysilane, and the like;

Examples of a modifier having a functional group represented by formula(k) may include 1,3-dimethyl-2-imidazolidinone and1,3-diethyl-2-imidazolidinone;

Examples of a modifier having a functional group represented by formula(1) may include N,N′-dimethylpropyleneurea and N-methylpyrrolidone;

wherein modified hydrogenated copolymers (2) having functional groupsrepresented by formulas (m) and (n) are obtained by hydrogenatingmodified unhydrogenated copolymers (2) having functional groupsrepresented by formulas (k) and (l), respectively.

Depending on the type of the modifier, when the modifier is reacted, ahydroxy group, an amino group, and the like may generally becomeorganometallic salts. In this case, these salts can be converted into ahydroxy group, an amino group, and the like by treating them with acompound having active hydrogen such as water or alcohol.

The hydrogenation catalyst used to produce a hydrogenated copolymer (1)and a modified hydrogenated copolymer (2) is not particularly limitedand the following catalysts, which have been known, are used: (1)supported nonuniform hydrogenation catalysts where a metal such as Ni,Pt, Pd, or Ru is supported on carbon, silica, alumina, siliceous earth,or the like; (2) so-called Ziegler hydrogenation catalysts using anorganic salt of Ni, Co, Fe, Cr, or the like or a transition metal saltsuch as acetylacetone salt and a reducing agent such as organoaluminum;and (3) uniform hydrogenation catalysts including a so-calledorganometallic complex such as an organometallic compound of Ti, Ru, Rh,Zr, or the like, and so on.

As specific hydrogenation catalysts, the hydrogenation catalystsdescribed in Japanese Patent Publication No. 42-8704, Japanese PatentPublication No. 43-6636, Japanese Patent Publication No. 63-4841,Japanese Patent Publication No. 1-37970, Japanese Patent Publication No.1-53851, and Japanese Patent Publication No. 2-9041 can be used.Preferable hydrogenation catalysts may include a mixture with atitanocene compound and/or a reducing organometallic compound. As atitanocene compound, the compound described in Japanese Patent Laid-OpenNo. 8-109219 can be used. Specific examples thereof may includecompounds having at least one ligand having a (substituted)cyclopentadienyl structure, an indenyl structure, or a fluorenylstructure, such as biscyclopentadienyltitanium dichloride andmonopentamethylcyclopentadienyltitanium trichloride. In addition,examples of a reducing organometallic compound may includeorganoalkaline metal compounds such as organolithium, organomagnesiumcompounds, organoaluminum compounds, organoboron compounds, andorganozinc compounds.

Hydrogenation reaction is generally performed in the temperature rangeof from 0 to 200° C., and more preferably from 30 to 150° C. It isrecommended that the hydrogen pressure used for hydrogenation reactionbe preferably 0.1 to 15 MPa, more preferably 0.2 to 10 MPa, and muchmore preferably 0.3 to 5 MPa. In addition, hydrogenation reaction timeis usually 3 minutes to 10 hours, preferably 10 minutes to 5 hours.Hydrogenation reaction can be performed in a batch process, in acontinuous process, or in combination thereof.

The hydrogenated copolymer (1) and the modified hydrogenated copolymer(2) can be separated from the solvent by removing the catalyst residuefrom the reaction solution after hydrogenation reaction as needed.Examples of a separation method for this purpose may include a methodwhich precipitates polymers by adding a polar solvent that is a poorsolvent for the polymers, such as acetone or alcohol, to the solutionafter hydrogenation and recovers the polymers, a method which places asolution of the hydrogenated copolymer (1) and the modified hydrogenatedcopolymer (2) in boiled water under stirring to remove the solvent bysteam stripping and recovers the polymers, and a method which directlyheats a polymer solution to distil away the solvent.

Moreover, various stabilizers such as phenolic stabilizers, phosphorousstabilizers, sulfur stabilizers, and amine stabilizers can be added tothe hydrogenated copolymer (1) and the modified hydrogenated copolymer(2).

If styrene-ethylene/butylene-styrene (SEBS) that is a styrenehydrogenated thermoplastic elastomer having a block structure is usedinstead of the hydrogenated copolymer (1) and/or the modifiedhydrogenated copolymer (2), the zinc oxide (3) cannot be mixed in largeamounts because of the presence of crystals in the ethylene/butylenepart, providing poor thermal conductivity. In addition, if a differentthermoplastic resin, such as a polypropylene resin, is used, theflexibility the thermally conductive material is required to have ispoor as well as the thermal conductivity is also poor because the zincoxide (3) cannot be mixed in large amounts.

The zinc oxide (3) is a zinc oxide having a core part and acicularcrystal parts extending from the core part in four different axialdirections. Examples thereof may include Pana-Tetra (trade name) fromAMTEC Co., Ltd. For such a zinc oxide having a core part and acicularcrystal parts extending from the core part in four different axialdirections, many contacts of the zinc oxide in a resin are produced,allowing a heat conduction path to be easily formed and therebyexcellent thermal conductivity to develop.

In addition, the zinc oxide (3) has a relatively greater particle sizethan other fillers have, and a greater area in contact with thehydrogenated copolymer (1) and/or the modified hydrogenated copolymer(2) due to crystals extending in four different axial directions, makingit difficult for the zinc oxide to fall because of the anchor effect.For these reasons, it is possible to reduce chips during fabricationgreatly and thereby reduce the failure of electronic substrates due topoor insulation.

The diameter of the base of acicular crystal parts in the zinc oxide (3)is preferably 0.7 to 14 μm, and the length between the base of acicularcrystal parts and an end thereof is preferably 3 to 200 μm. The diameterof the base of acicular crystal parts is more preferably 1 to 14 μm andthe length between the base of acicular crystal parts and an end thereofis more preferably 10 to 200 μm. Here, the diameter of the base refersto the diameter of acicular crystal parts in the joints between a corepart and the acicular crystal parts.

In the structure of the zinc oxide (3), the angle between one of theacicular crystal parts extending from the core part which is used asreference and each of the other acicular crystal parts extending indirections different from the direction in which the acicular crystalpart extends is preferably in a range of from 90° to 140°, morepreferably in a range of from 100° to 120°. The angle is most preferably109.5° at which the acicular crystal parts extend in equally spaceddirections like a tetrapod.

The zinc oxide (3) according to the present invention also includes azinc oxide having a core part and acicular crystal parts extending fromthe core part in four different axial directions where the zinc oxide issurface-treated with a coupling agent. As such a coupling agent, asilane coupling agent, a titanate coupling agent, an aluminum couplingagent are preferably used.

In addition, the thermally conductive material according to the presentinvention may contain an acicular zinc oxide, but this type of acicularzinc oxide is caused by the breakage of the acicular crystal partsextending in four axial directions of the zinc oxide (3), without anydamage to the major characteristics of the present invention.

The use of the zinc oxide (3) provides better thermal conductivity thanthe use of amorphous and spherical zinc oxides. Also, the use of thezinc oxide (3) makes it difficult to produce chips and thereby causepoor insulation.

However, zinc oxides other than the zinc oxide (3), such as granularzinc oxide and spherical zinc oxide, can also be used in amounts that donot impair the object of the present invention.

The paraffin oil (4) refers to a lubricant base oil obtained byhydrogenating and refining a petroleum fraction or residual oil orcracking it where the number of carbon atoms of the paraffin chainsaccounts for 50% or more of all carbon atoms. When a thermallyconductive material or a thermally conductive sheet is produced, theparaffin oil (4) is used to mix the zinc oxide (3) in large amounts andto provide a thermally conductive material obtained by melting andkneading and a thermally conductive sheet molded from the thermallyconductive material with higher thermal conductivity and give themflexibility.

The kinematic viscosity of the paraffin oil (4) at 40° C. is 100 mm²/sor more, preferably 100 to 10,000 mm²/s, and much more preferably 200 to5,000 mm²/s.

Examples of the paraffin oil (4) may include NA Solvent (trade name)from Nippon Oil & Fats Co., Ltd., Diana (registered trademark) ProcessOils PW-90 and PW-380 from Idemitsu Kosan Co., Ltd., IP Solvent 2835(trade name) from Idemitsu Petrochemical Co., Ltd., and Neotiozol (tradename) from Sanko Kagaku Kogyo K.K.

In addition to the paraffin oil (4), naphthenic oils where the number ofcarbon atoms in the naphthene ring is 30 to 45%, aromatic oils where thenumber of aromatic carbon atoms exceeds 30%, castor oil, linseed oil,polybutene, low-molecular-weight polybutadiene, liquid paraffin, or thelike can be used to provide flexibility in amounts that do not impairthe object of the present invention.

Examples of the flame retardant (5) may include halogen-based flameretardants, metal hydroxide-based flame retardants, phosphorus-basedflame retardants, and silicon-based flame retardants.

Examples of the halogen-based flame retardants may include thefollowing.

Examples of chlorine-based flame retardants may include chlorinatedparaffin, chlorinated polyethylene, and perchlorocyclopentadecane.

Examples of bromine-based flame retardants may includehexabromocyclododecane (HBCD), decabromodiphenyloxide (DBDPO),octabromodiphenyloxide, tetrabromobisphenol A (TBBA),bis(tribromophenoxy)ethane, bis(pentabromophenoxy)ethane (BPBPE),tetrabromobisphenol A epoxy resin (TBBA epoxy), tetrabromobisphenol Acarbonate (TBBA-PC), ethylene(bistetrabromophthal)imide (EBTBPI),ethylenebispentabromodiphenyl, tris(tribromophenoxy)triazine (TTBPTA),bis(dibromopropyl)tetrabromobisphenol A (DBP-TBBA),bis(dibromopropyl)tetrabromobisphenol S (DBP-TBBS), tetrabromobisphenolS (TBBS), tris(tribromoneopentyl)phosphate (TTBNPP),polybromotrimethylphenylindane (PBPI), andtris(dibromopropyl)-isocyanurate (TDBPIC).

Among the halogen-based flame retardants above, bromine-based flameretardants are preferable to allow the flame retardancy of the thermallyconductive material according to the present invention to develop whenthey are added in small amounts. To improve the dispersion of the flameretardants, bromine-based flame retardants having a melting point of 50to 150° C. are more preferable. To prevent the bleed-out of the flameretardants, bis(dibromopropyl)tetrabromobisphenol A (DBP-TBBA) is muchmore preferable.

Examples of the metal hydroxide-based flame retardants may includemagnesium hydroxide and aluminum hydroxide. Surface-treated metalhydroxides can also be used. Specific examples thereof may includemagnesium hydroxide and aluminum hydroxide which are surface-treatedwith stearic acid, fatty acid, titanic acid, a silane coupling agent, anitric compound, or the like. Among these, aluminum hydroxidesurface-treated with a nitric compound is more preferable. This isbecause aluminum hydroxide is non-halogen-based and non-phosphorous,allowing environmentally-friendly flame retardancy to develop, a morehighly endothermic reaction at low temperature to take place than othermetal hydroxide flame retardants, flame retardancy to develop with theuse of a small amount, and flexibility and toughness to be retained.Examples of the nitric compound used here may include methyl nitrate,ethyl nitrate, butyl nitrate, isopropyl nitrate, isobutyl nitrate,ammonium nitrate, lithium nitrate, sodium nitrate, potassium nitrate,cesium nitrate, magnesium nitrate, calcium nitrate, iron nitrate, nickelnitrate, copper nitrate, zinc nitrate, guanidine nitrate, cellulosenitrate, hydroxyammonium nitrate, methyl nitrite, ethyl nitrite, butylnitrite, isopropyl nitrite, isobutyl nitrite, ammonium nitrite, lithiumnitrite, sodium nitrite, potassium nitrite, cesium nitrite, magnesiumnitrite, calcium nitrite, iron nitrite, nickel nitrite, copper nitrite,and zinc nitrite. Two or more of these nitric compounds may be mixed.Ammonium nitrate is more preferable in view of degradation temperatureand resin coloration protection. Examples of the aluminum hydroxidesurface-treated with a nitric compound may include Pyrolyzer (registeredtrademark) HG (aluminum hydroxide surface-treated with ammonium nitrate)from Ishizuka Glass Co., Ltd.

The average particle size of the metal hydroxide-based flame retardantsis preferably in a range of from 0.1 μm to 5 μm, and more preferably ina range of from 0.5 μm to 3 μm, in view of mechanical strength andtoughness retention.

Examples of the phosphorus-based flame retardants may includephosphazene compounds, phosphate ester, condensed phosphate ester,phosphinate, and tertiary phosphines, and further include redphosphorus-based compounds, phosphonate, phosphate ester amide,phosphorus-containing polymers, phosphine oxide, and phosphine sulfide.

Among the phosphorus-based flame retardants above, phosphazene compoundsare preferable in view of flame retardancy and safety. These compoundscan be used alone or as a mixture of two or more of them.

The water content of the phosphorus-based flame retardants is preferably1000 ppm or less, more preferably 800 ppm or less, much more preferably650 ppm or less, still more preferably 500 ppm or less, and yet morepreferably 300 ppm or less, in view of electrical characteristics,hydrolysis resistance, and the like. The acid value as determinedaccording to JIS K6751 is preferably 1.0 or less, and more preferably0.5 or less.

In addition, the water solubility (solubility after a sample is mixedinto distilled water at a concentration of 0.1 g/mL and the mixture isstirred at room temperature for 1 hour) of the phosphorus-based flameretardants is preferably 100 ppm or less, more preferably 50 ppm orless, and much more preferably 25 ppm or less, in view of hydrolysisresistance and moisture absorption resistance.

With the phosphorus-based flame retardants, when they are heated in aninert gas atmosphere at a rate of temperature rise of 10° C./min fromroom temperature to 600° C., the difference between the temperature atwhich a decrease in mass is 50 mass % and the temperature at which adecrease in mass is 5 mass %, as determined according tothermogravinetric analysis (TGA), is preferably 20 to 150° C., and morepreferably 20 to 120° C., in view of flame retardancy, low smokeemission during burning, low volatility, and the like. If thephosphorus-based flame retardants are used for resins, the temperatureat which a decrease in mass is 50 mass. % is preferably 320 to 500° C.,and more preferably 350 to 460° C., in view of flame retardancyefficiency due to the effect of accelerating char layer formation duringburning.

The phosphorus-based flame retardants can also take various forms suchas liquid form, wax form, and solid form, depending on the differencesin the type and structure of the substituent group contained. Any formis possible unless it impairs the advantages of the present invention.

If the heat resistance and low volatility of the phosphorus-based flameretardants themselves need to be considered, phosphazene compounds,phosphate ester, condensed phosphate ester, tertiary phosphines, andphosphinate are more preferably used among the phosphorus-based flameretardants that can preferably be used for the present invention. Ifhydrolysis resistance further needs to be considered, phosphazenecompounds are more preferably used.

Any known phosphazene compounds can be widely used. The structure ofphosphazene compounds preferably used for the present invention isdescribed, for example, in James E. Mark, Harry R. Allcock, Robert West,Inorganic Polymers, Prentice Hall International, Inc., 1992, pp. 61-140.Examples of the phosphazene compounds may include cyclic phosphazenecompounds represented by the following general formula (1) and/or chainphosphazene compounds represented by the following general formula (2).Among them, compounds containing 95 mass % or more of phosphazenecompounds having these structures are preferable.

(wherein n is an integer of 3 to 25, and m is an integer of 3 to 10,000.The substituent group X's represent a substituent group selected fromthe substituent groups represented by an alkyl group having a carbonnumber of 1 to 6, an aryl group having a carbon number of 6 to 11, afluorine atom, an aryloxy group having a substituent group representedby the following general formula (3), a naphthyloxy group, and an alkoxygroup and alkoxy-substituted alkoxy group having a carbon number of 1 to6, and they may be different or the same. Part or the whole of thehydrogen on the substituent group may be substituted with fluorine. Inaddition, Y in the lower formula represents —N═P(O)(X) or —N═P(X)₃, andZ represents —P(X)₄ or —P(O)(X)₂.)

(wherein Y₁, Y₂, Y₃, Y₄, and Y₅ independently represent a substituentgroup selected from the group consisting of a hydrogen atom, a fluorineatom, an alkyl or alkoxyl group having a carbon number of 1 to 5, aphenyl group, and hetero element-containing groups.)

Examples of the substituent group X in the phosphazene compounds mayinclude alkyl groups such as a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an s-butyl group, atert-butyl group, an n-amyl group, and an isoamyl group; aryl groupssuch as a phenyl group, 2-methylphenyl group, 3-methylphenyl group,4-methylphenyl group, 2,6-dimethylphenyl group, 3,5-dimethylphenylgroup, 2,5-dimethylphenyl group, 2,4-dimethylphenyl group,3,4-dimethylphenyl group, 4-tert-butylphenyl group, and2-methyl-4-tert-butylphenyl group; alkoxy groups such as a methoxygroup, an ethoxy group, an n-propyloxy group, an isopropyloxy group, ann-butyloxy group, a tert-butyloxy group, an s-butyloxy group, ann-amyloxy group, an isoamyloxy group, a tert-amyloxy group, and ann-hexyloxy group; alkoxy-substituted alkoxy groups such as amethoxymethoxy group, a methoxyethoxy group, a methoxyethoxymethoxygroup, a methoxyethoxyethoxy group, and a methoxypropyloxy group;alkyl-substituted phenoxy groups such as a phenoxy group, a2-methylphenoxy group, a 3-methylphenoxy group, a 4-methylphenoxy group,a 2,6-dimethylphenoxy group, a 2,5-dimethylphenoxy group, a2,4-dimethylphenoxy group, a 3,5-dimethylphenoxy group, a3,4-dimethylphenoxy group, a 2,3,4-trimethylphenoxy group, a2,3,5-trimethylphenoxy group, a 2,3,6-trimethylphenoxy group, a2,4,6-trimethylphenoxy group, a 2,4,5-trimethylphenoxy group, a3,4,5-trimethylphenoxy group, a 2-ethylphenoxy group, a 3-ethylphenoxygroup, a 4-ethylphenoxy group, a 2,6-diethylphenoxy group, a2,5-diethylphenoxy group, a 2,4-diethylphenoxy group, a3,5-diethylphenoxy group, a 3,4-diethylphenoxy group, a4-n-propylphenoxy group, a 4-isopropylphenoxy group, a4-tert-butylphenoxy group, a 2-methyl 4-tert-butylphenoxy group, a2-phenylphenoxy group, a 3-phenylphenoxy group, and a 4-phenylphenoxygroup; and an aryl-substituted phenoxy group, a naphthyl group, and anaphthyloxy group. Part or the whole of the hydrogen in these groups maybe substituted with fluorine and/or a hetero element-containing group.

The hetero element-containing group refers to a group containing a B, N,O, Si, P, or S atom. Examples thereof may include a group containing anamino group, an amide group, an aldehyde group, a glycidyl group, acarboxy group, a hydroxy group, a mercapto group, a silyl group, or thelike.

Moreover, these phosphazene compounds may be cross-linked with acrosslinking group selected from the group consisting of a phenylenegroup, a biphenylene group, and a group represented by the followingformula (4) by means of the technique disclosed in InternationalPublication No. WO00/09518.

(wherein Xq represents —C(CH₃)₂—, —SO₂—, —S—, or —O—, and y represents 0or 1.)

Specifically, these phosphazene compounds having a crosslinked structureare produced by reacting an alkali metal salt of a phenol and an alkalimetal salt of an aromatic dihydroxy compound with a dichlorophosphazeneoligomer. These alkali metal salts are added to the dichlorophosphazeneoligomer in an amount that is slightly more than the theoretical amount.

These compounds may be used alone or as a mixture of two or more ofthem.

A contributing factor to flame retardancy is the concentration ofphosphorus atoms contained in molecules. In phosphazene compounds, chainphosphazene having a chain structure has a lower phosphorus content thancyclic phosphazene compounds because of the presence of a substituentgroup at a molecular end. For this reason, if the same weight is added,it seems that cyclic phosphazene compounds can provide a higher flameretardancy than chain phosphazene compounds. In the present invention,therefore, phosphazene compounds having a cyclic structure arepreferably used and flame retardants containing having 95 mass % or moreof cyclic phosphazene compounds are preferable.

In addition, a phosphazene compound is a mixture of compounds havingdifferent structures including ring compounds such as a cyclic trimerand a cyclic tetramer and chain phosphazene. If a phosphazene compoundis added to a resin, a higher content of a cyclic trimer and a cyclictetramer tends to provide a more preferable processability to the resin.Specifically, a phosphazene compound preferably contains 80 mass % ormore of cyclic trimer and/or tetramer compounds, more preferably 85 mass% or more of trimer and/or tetramer compounds, and much more preferably93 mass % or more of trimer and/or tetramer compounds.

In addition, in the present invention, if a phosphazene compoundcontaining preferably 70 mass % or more of a trimer, more preferably 76mass % or more of a trimer, much more preferably 80 mass % or more of atrimer, or still more preferably 85 mass % or more of a trimer is used,the phosphazene compound provides especially good flame retardancy andfurther improves good mechanical characteristics.

In addition, a phosphazene compound can take various forms such asliquid form, wax form, and solid form, depending on the differences inthe type and structure of the substituent group, and any form ispossible unless it impairs the advantages of the present invention. Insolid form, the bulk density is preferably 0.45 g/cm³ or more, and morepreferably 0.45 g/cm³ or more and 0.75 g/cm³ or less.

The content of each of the alkali metal components such as sodium andpotassium contained in the hosphazene compound is preferably 200 ppm orless, more preferably 50 ppm or less, and much more preferably, thecontent of all alkali metal components is 50 ppm or less.

In addition, in the phosphazene compound, a phosphazene compound whereat least one of the substituent groups X in the general formula (1) is ahydroxy group, in other words, the content of a phosphazene compoundcontaining a P—OH bond is preferably less than 1 mass %, and thechlorine content is preferably 1000 ppm or less, more preferably 500 ppmor less, and much more preferably 300 ppm or less.

The phosphazene compound where at least one of the substituent groups Xis a hydroxy group may contain an oxo-form structure represented by thefollowing general formula (5). However, the content of a phosphazenecompound having this oxo-form structure is preferably less than 1 mass%. The same holds true for phosphazene compounds having a chainstructure represented by the above general formula (2).

(wherein each of a and b is an integer and its sum (a+b) is an integerof 3 or more. In addition, X in the formula may be the same ordifferent.)

Known phosphate esters can be used. Examples of thereof may includetriphenyl phosphate, triphenyl phosphate, tricresyl phosphate,tryxylenyl phosphate, cresyl diphenyl phosphate, xylenyl diphenylphosphate, dixylenyl phenyl phosphate, cresyl dixylenyl phosphate, anddicresyl xylenyl phosphate.

Examples of condensed phosphate esters may include pentaerythritoldiphosphate and phosphate ester-based compounds having the followinggeneral formula (6) or (7). A condensed phosphate ester synthesized withbisphenol A and phenol as raw materials and a condensed phosphate esterobtained with bisphenol A or resorcin and 2,6-xylenol as raw materialsare more preferable.

(wherein Q₁, Q₂, Q₃, Q₄, Q₉, Q₁₀, Q₁₁, and Q₁₂ independently represent ahydrogen atom or an alkyl group having a carbon number of 1 to 6 and Q₅,Q₆, Q₇, Q₈, and independently represent a hydrogen atom or a methylgroup. m1, m2, m3, m4, m7, m8, m9, and m10 independently represent aninteger of 0 to 3, m5 and m6 independently represent an integer of 0 to2, and m11 independently represents an integer of 0 to 4.)

Examples of phosphinate may include at least one selected fromphosphinates represented by the following general formula (8) and/or (9)and/or these polymers.

(wherein Q₁, Q₂, Q₃, and Q₄ independently represent a group selectedfrom a hydrogen atom, and an alkyl group having a carbon number of 1 to12, an alkoxy group, an aryl group, and an aryloxy group having a carbonnumber of 1 to 12, Q₅ represents a group selected from alkylene,arylalkylene, arylene, alkylarylene, and diarylene having a carbonnumber of 1 to 18. Each of n and m is an integer of 1 to 3 and x is 1 or2. In addition, M represents a metal atom in the fourth and subsequentrows of the periodic table or a group selected from amide, an ammoniumgroup and a melamine derivative, and if x is 2, the group may be thesame or different.)

Known tertiary phosphines can be preferably used. Examples of thereofmay include triarylphosphine, trialkylphosphine, triaryloxyphosphine,trialkoxyphosphine, bis(diarylphosphino)benzene, andtris(diarylphosphino)benzene. The temperature at which a decrease inmass is 10 mass % when such a tertiary phosphine is heated in an inertgas atmosphere at a rate of temperature rise of 10° C./min from roomtemperature to 600° C., as determined according to TGA, is preferably150° C. to 320° C. in view of a balance between heat resistance as wellas flame retardancy and mechanical characteristics. Specifically,triarylphosphine, trialkylphosphine, triaryloxyphosphine, andtrialkoxyphosphine are preferable and triarylphosphines represented bythe following general formula (10) are more preferable.

(wherein T₁, T₂, T₃, and T₄ independently represent a hydrogen atom oran alkyl or aryl group having a carbon number of 1 to 12, and T₅represents a hydrogen atom or a methyl group. m1, m2, m3, and m4independently represent an integer of 0 to 5, and m5 independentlyrepresents an integer of 0 to 4. In addition, n in the formularepresents an integer of 0 to 3. In addition, a naphthyl group can bepreferably used as an aryl group. Moreover, the three aryl groups on aphosphorus atom may be all the same or different from one another.)

In the present invention, an antimony-based compound can be used with aflame retardant. Examples of the antimony-based compound may includeantimony oxides such as antimony trioxide, antimony tetroxide, andantimony pentoxide; and sodium antimonate.

Furthermore, if thermal conductivity is to be improved, a filler (6) canbe added. The filler (6) refers to a filler having a thermalconductivity of from 10 to 400 W/m·K and excludes the zinc oxide (3).Examples of the filler (6) may include metal powders, metal nitrides,metal carbides, metal oxides, and carbon compounds. More specifically,

-   Metal powders: gold, silver, copper, aluminum, copper-aluminum    alloy, copper-tin alloy, aluminum-tin alloy, and the like;-   Metal nitrides: silicon nitride, aluminum nitride, boron nitride,    and the like;-   Metal carbides: silicon carbide, aluminum carbide, boron carbide,    and the like;-   Metal oxides: zinc oxide, magnesium oxide, aluminum oxide, silicon    dioxide, and the like; and-   Carbon compounds: graphite, black lead, Ketjen black, carbon fiber,    CNT, and the like.

Among the filler examples, silicon nitride, aluminum nitride, siliconcarbide, boron nitride, and graphite are preferable in view of thermalconductivity, electrical insulation control, and compounding handling,safety, and the like; and graphite, aluminum nitride, or boron nitrideis more preferable in view of thermal conductivity. Aluminum nitride orboron nitride is more preferable in view of thermal conductivity andelectrical insulation.

If graphite is used, various natural graphites or artificial graphitescan be used. As natural graphites, flake graphite, massive graphite, andearthy graphite can be used. Expanded graphite produced by inserting(intercalating) sulfuric acid or the like between layers of flakegraphite or the like, heating at a temperature of from 800 to 1000° C.,and expanding the intralayer distance greatly can also be used. Theshape of graphite used is preferably spherical in view of toughness. Inaddition, the average particle size of the filler (6) that can be usedin the present invention is preferably 0.5 μm or more and 100 μm orless, and more preferably 0.5 μm or more and 50 μm or less. Much morepreferably, if the filler (6) is aluminum nitride, its average particlesize is 0.5 μm or more and 2 μm or less and if the filler (6) is boronnitride, its average particle size is 0.8 μm or more and 30 μm or less.If the filler (6) is graphite, its average particle size is 25 μm ormore and 50 μm or less for higher thermal conductivity and 1 μm or moreand less than 25 μm for higher toughness.

In addition, the ratio T2/T1 of the thickness T1 (μm) of a thermallyconductive sheet molded from a thermally conductive material accordingto the present invention to the average particle size T2 (μm) of thezinc oxide (3) or the filler (6), whichever is greater, is preferably 1or less, more preferably 0.8 or less, and much more preferably 0.5 orless. If T2/T1 is 1 or less, particles of the zinc oxide (3) or thefiller (6) do not protrude from the surface of the sheet, keeping thesheet surface smooth. For this reason, even if the thermally conductivesheet is used in applications requiring electrical insulation such aselectronic substrates, it causes no problems such as the passage ofcurrent.

The purity of the filler (6) is preferably 90% or more, more preferably97% or more, and much more preferably 99% or more, in view of thermalconductivity and ease of control of electrical insulation.

In the thermally conductive material according to the present invention,for the content of the hydrogenated copolymer (1) and the modifiedhydrogenated copolymer (2), if a thermally conductive material havingexcellent adhesion is to be obtained, it is recommended that the contentof the modified hydrogenated copolymer (2) based on the total content ofthe hydrogenated copolymer (1) and the modified hydrogenated copolymer(2) be preferably 50 mass % or more, more preferably 70 mass % or more,and much more preferably 90 mass % or more. In addition, if a thermallyconductive material having excellent corrosion resistance is to beobtained, it is recommended that the content of the modifiedhydrogenated copolymer (2) be preferably 30 mass % or less, morepreferably 20 mass % or less, and much more preferably 10 mass % orless.

In the thermally conductive material according to the present invention,if it does not contain the paraffin oil (4), the total content of thehydrogenated copolymer (1) and the modified hydrogenated copolymer (2),[(1)+(2)], is 10 mass % or more and 90 mass % or less based on 100 mass% of the thermally conductive material. A total content [(1)+(2)] of 10mass % or more provides sufficient flexibility and toughness while 90mass % or less provides sufficient thermal conductivity.

The content of the zinc oxide (3) is 10 mass % or more and 90 mass % orless, preferably 50 mass % or more and 90 mass % or less, morepreferably 65 mass % or more and 90 mass % or less, and much morepreferably 70 mass % or more and 90 mass % or less based on 100 mass %of the thermally conductive material. However, if the flame retardant(5) is contained, the content of the zinc oxide (3) is 10 mass % or moreand 87 mass % or less, preferably 50 mass % or more and 87 mass % orless, more preferably 65 mass % or more and 87 mass % or less, and muchmore preferably 70 mass % or more and 87 mass % or less based on 100mass % of the thermally conductive material. Such a range providesexcellent heat dissipation, flexibility, and toughness.

The total content of the hydrogenated copolymer (1), the modifiedhydrogenated copolymer (2), and the paraffin oil (4), [(1)+(2)+(4)], is10 mass % or more and 90 mass % or less based on 100 mass % of thethermally conductive material. However, if the flame retardant (5) iscontained, the total content [(1)+(2)+(4)] is 10 mass % or more and 87mass % or less based on 100 mass % of the thermally conductive material.In either case, the range provides good flexibility and toughness aswell as good thermal conductivity. The total content [(1)+(2)+(4)] ismore preferably 10 mass % or more and 60 mass % or less, and much morepreferably 10 mass % or more and 40 mass % or less.

In addition, the ratio of the mass of the paraffin oil (4) to the totalmass of the hydrogenated copolymer (1) and modified hydrogenatedcopolymer (2) used in the present invention, [(4)/{(1)+(2)}], is greaterthan 0 and 2 or less, preferably 0.5 or more and 1.5 or less, and morepreferably 0.8 or more and 1.2 or less. A mass ratio of 2 or less canprevent the bleed-out of the paraffin oil (4). The use of the paraffinoil (4) can provide higher flexibility and allow the zinc oxide (3) tobe mixed in larger amounts, thereby providing higher thermalconductivity.

In addition to satisfying the above content and ratio, the content ofthe paraffin oil (4) is preferably 0 mass % or more and 90 mass % orless based on 100 mass % of the thermally conductive material. Thecontent is more preferably 0 mass % or more and 50 mass % or less, andmuch more preferably 0 mass % or more and 20 mass % or less.

The content of the flame retardant (5) used in the present invention is3 mass % or more and 30 mass % or less based on 100 mass % of thethermally conductive material. The content is preferably 3 mass % ormore and 20 mass % or less, and more preferably 3 mass % or more and 15mass % or less. A content of 30 mass % or less can provide sufficientthermal conductivity, whereas a content of 3 mass % or more can provideflame retardancy.

The ratio of the mass of the flame retardant (5) to the total mass ofhydrogenated copolymer (1), the modified hydrogenated copolymer (2), andthe paraffin oil (4), [(5)/{(1)+(2)+(4)}], is preferably 0.2 or more and3 or less, more preferably 0.4 or more and 3 or less, much morepreferably 0.6 or more and 2.5 or less, and most preferably 1 or moreand 2 or less. A mass ratio of 0.2 or more can provide flame retardancy,whereas a mass ratio of 3 or less can provide sufficient flexibility andtoughness.

If the flame retardant (5) is not contained, the total content of thezinc oxide (3) and the filler (6), [(3)+(6)], is preferably 10 mass % ormore and 90 mass % or less based on 100 mass % of the thermallyconductive material. The total content is more preferably 50 mass % ormore and 90 mass % or less, much more preferably 65 mass % or more and90 mass % or less, and most preferably 70 mass % or more and 90 mass %or less.

If the flame retardant (5) is contained, the total content [(3)+(6)] ispreferably 10 mass % or more and 87 mass % or less based on 100 mass %of the thermally conductive material. The content is more preferably 50mass % or more and 87 mass % or less, much more preferably 65 mass % ormore and 87 mass % or less, and most preferably 70 mass % or more and 87mass % or less. Such a range provides excellent heat dissipation,flexibility, and toughness.

The ratio of the mass of the filler (6) to the total mass [(3)+(6)] ofthe zinc oxide (3) and the filler (6) is preferably greater than 0 andless than 0.5, more preferably 0.1 or more and 0.3 or less, and muchmore preferably 0.1 or more and 0.15 or less. If the ratio of the massof the filler (6) to the total mass [(3)+(6)] is 0.5 or less, thermalconductivity increases because of the contact of the filler (6) with thezinc oxide (3) and the like.

Here, the effects of the filler (6) on thermal conductivity andelectrical insulation vary because conditions such as how the filler (6)comes into contact with the zinc oxide (3) vary depending on the type,shape, particle size, and particle size distribution of the filler (6)used. To satisfy electrical insulation that a thermally conductivematerial and a thermally conductive sheet molded therefrom are requiredto have in electric and electronic applications, the content of thefiller (6) is selected from a range of the ratio of the mass of thefiller (6) to the total mass [(3)+(6)] of the zinc oxide (3) and thefiller (6) between 0 or more and less than 0.5 so that volumeresistivity at an applied voltage of 100 V is 1×10⁸ Ω·cm or more andless than 1×10¹⁶ Ω·cm.

In addition to satisfying the content and ratio above, the content ofthe filler (6) is 0 mass % or more and less than 45 mass % based on 100mass % of the thermally conductive material. The content is morepreferably 3 mass % or more and less than 45 mass %, and much morepreferably 8 mass % or more and less than 45 mass %.

The thermally conductive material according to the present invention maycontain additives such as a polymer made only from a vinyl aromatic, anacrylic-based resin, a fatty acid, a fatty acid salt, an anti-drip agentas a flame retardant aid, an antioxidant, an ultraviolet absorber, arigidity improver, a thermal stabilizer, an antistatic agent, a lightstabilizer, an antiaging agent, and a colorant as needed unless thematerial impairs the object of the present invention.

The acrylic-based resin refers specifically to a polymer or copolymer ofat least one compound selected from the group consisting of(meth)acrylic acid alkyl ester. Examples of the (meth)acrylic acid alkylester may include methyl acrylate, methyl methacrylate, ethyl acrylate,ethyl methacrylate, n-propyl acrylate, n-butyl acrylate, 2-ethyl hexylacrylate, and hexyl methacrylate, 2-ethyl hexyl methacrylate, anddodecyl methacrylate. As an acrylic-based resin, each of these compoundscan be used alone or if it is a copolymer obtained by polymerizing acombination of two or more of them. In addition, a graft copolymerobtained by grafting poly(alkyl)methacrylate on acrylic-based rubberparticle obtained by polymerizing acrylic acid alkyl ester can also beused. Examples of the copolymer may include Hiblen (trade name) fromZeon KASEI Co., Ltd.

The content of an acrylic-based resin is greater than 0 and 5 mass % orless, more preferably 0.01 mass % or more and 5 mass % or less, and muchmore preferably 0.05 mass % or more and 2 mass % or less, based on 100mass % of the thermally conductive material. The addition of anacrylic-based resin can reduce the anisotropy in the direction of heatconduction and greatly reduce variation in the thickness of sheetsformed by calendering or the like. However, if the content of theacrylic-based resin exceeds 5 mass %, thermal conductivity decreases.

The fatty acid and fatty acid salt may be a saturated fatty acid and asaturated fatty acid salt or an unsaturated fatty acid and anunsaturated fatty acid salt. A carbon number of 8 to 34 is morepreferable and a carbon number of 14 to 22 is much more preferable. Inaddition, a saturated fatty acid and a saturated fatty acid salt arepreferable. Examples thereof may include fatty acids such as lauricacid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid,heptadecylic acid, stearic acid, nonadecanoic acid, oleic acid, capricacid, behenic acid, linoleic acid, and montanoic acid and alkaline earthmetal salts of these acids such as magnesium salt, calcium salt, andbarium salt as well as zinc metal salts of the acids. Among these,stearic acid, oleic acid, and lauric acid, alkaline earth metal salts ofthese acids (magnesium salt and calcium salt), and zinc metal salts ofthe acids are preferably used.

The total content of the fatty acid and the fatty acid salt ispreferably greater than 0 and 5 mass % or less, 0.2 mass % or more and 3mass % or less, and much more preferably 0.5 mass % or more and 2 mass %or less, based on 100 mass % of the thermally conductive material. Theaddition of a fatty acid and a fatty acid salt greatly increases theproperties of releasing a sheet from the rollers at high temperature inT-die sheet forming and calendering. These good sheet release propertiesprovide a thermally conductive sheet having excellent smoothness, andwhen the resulting thermally conductive sheet is placed on an electronicsubstrate, this smoothness increases adhesion and thus greatly improvesthermal conductivity. The addition also greatly reduces variation in thethickness of a thermally conductive sheet formed by calendering or thelike. If the content of a fatty acid and a fatty acid salt is 5 mass %or less, sufficient thermal conductivity is also retained.

As a flame retardant aid, an anti-drip agent such aspolytetrafluoroethylene can also be added. The molecular weight of thispolytetrafluoroethylene is 10×10⁴ or more, preferably about 20×10⁴ to300×10⁴. A molecular weight of 10×10⁴ or more inhibits a thermallyconductive material containing polytetrafluoroethylene from dripping atburning. Examples of the polytetrafluoroethylene may include Metablen(registered trademark) from Mitsubishi Rayon Co., Ltd.

Examples of the antioxidant that can be used in the present inventionmay include hindered phenol-based antioxidants, amine-based andhydroxylamine-based antioxidants. Examples of the hindered phenol-basedantioxidants may include triethyleneglycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate], andpentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate].

Examples of the ultraviolet absorber that can be used in the presentinvention may include benzotriazole-based ultraviolet absorbers,benzophenone-based ultraviolet absorbers, salicylate-based ultravioletabsorbers, cyanoacrylate-based ultraviolet absorbers, and nickel complexsalt ultraviolet absorbers. Benzotriazole-based ultraviolet absorbersand benzophenone-based ultraviolet absorbers are particularlypreferable.

To increase the mechanical strength of the thermally conductive materialaccording to the present invention, rigidity improvers such as calciumcarbonate and magnesium carbonate can be used.

For the electrical insulation of the thermally conductive materialaccording to the present invention and a thermally conductive sheetmolded therefrom, if the volume resistivity at an applied voltage of 100V is 1×10⁸ Ω·cm or more and less than 1×10¹⁶ Ω·cm, built-up staticelectricity or the passage of current does not break electronic parts orthe like. The volume resistivity is preferably 1×10¹⁰ Ω·cm or more andless than 1×10¹⁶ Ω·cm, and more preferably 1×10¹² Ω·cm or more and lessthan 1×10¹⁶ Ω·cm. In addition, the applied voltage at which the volumeresistivity is 1×10⁸ Ω·cm or more and less than 1×10¹⁶ Ω·cm ispreferably 100 V or more, more preferably 250 V or more, much morepreferably 500 V or more, and most preferably 1 kV or more.

The thermally conductive material according to the present invention caneasily be produced by a traditional known technique such as a Brabender,a kneader, a Banbury mixer, or a twin or single screw extruder.

The thermally conductive material according to the present invention hasexcellent thermal conductivity and is thermoplastic, so it can be meltedand injected into a mold into the desired shape. For this reason, thethermally conductive material according to the present invention ispreferably used as molded bodies in various heat dissipationapplications.

Molded bodies having such characteristics are obtained by heating,melting, plasticating, and molding the thermally conductive materialaccording to the present invention into the desired shape. Specifically,they can be produced by known molding processes such as injectionmolding, injection press molding, or gas injection molding.

Among them, molded bodies in sheet form are preferable because thethermally conductive material according to the present invention isthermoplastic, melt which has been heated and plasticated can easily beshaped into a continuous thin-walled sheet, there are little amounts ofvolatile components due to heating, and the like.

After keading by the above technique, a thermally conductive sheetmolded from the thermally conductive material according to the presentinvention can be produced by a process such as T-die sheet forming,calendering, blow molding, press molding, or blown film extrusion as afabrication process other than injection molding, injection pressmolding, and gas injection molding. Among the processes, T-die sheetforming or blown film extrusion is preferable to produce a thermallyconductive sheet formed from a thermally conductive material having athickness of 0.2 mm or less. To produce a thermally conductive sheethaving excellent surface smoothness, calendering or press molding ispreferable. When a thermally conductive sheet having excellent surfacesmoothness is placed on a heating body, the material adheres closely tothe heating body and a cooling part and thus brings both close to eachother, providing excellent heat dissipation.

Specifically, for the smoothness of the thermally conductive sheet, the60° surface gloss on the surface of the thermally conductive sheetmolded from the thermally conductive material as determined according toJIS K7105 is preferably 10 or more.

The thickness of the thermally conductive sheet molded from thethermally conductive material according to the present invention ispreferably 30 μm or more and 3 cm or less. A thickness of 30 μm or moreallows the electrical insulation to be retained, whereas a thickness of3 cm or less provides easy fabrication and handling. In addition, athicker thermally conductive sheet provides higher electrical insulationand flame retardancy.

In applications where heat from a heating body is required to dissipaterapidly, a thin sheet having a short path to conduct heat is preferable.Specifically, the thickness of the sheet is more preferably 30 μm ormore and 1 mm or less, and much more preferably 30 μm or more and 0.5 mmor less. In addition, in applications as a spacer between a heating bodysuch as a CPU and a cooling part such as a heatsink, a cushioned thicksheet is preferable. Specifically, the thickness of the sheet ispreferably greater than 1 mm and 3 cm or less and the JIS A hardness ofthe sheet is preferably 65 or less, and more preferably 45 or less. Thiscushioned thick thermally conductive sheet is preferable as a spacer(installed between the floor and circulation pipes) for house floorheating.

The JIS A hardness of the thermally conductive sheet molded from thethermally conductive material according to the present invention ispreferably 20 more and 95 or less. A hardness of 95 or less brings asemiconductor element and a cooling part sufficiently close to eachother, providing good thermal conductivity. A hardness of 20 or moreprovides easy handling.

The thermally conductive material according to the present invention andthe thermally conductive sheet molded from the thermally conductivematerial can be recycled in view of the prevention of environmentalproblems such as waste. Specifically, they can be recycled in thefollowing ways:

-   1) The thermally conductive sheets collected after they have once    been distributed to the market or the like are shredded as needed    and the thermally conductive material is added to the shredded    sheets, which are then melted and formed again into a sheet; or-   2) Collected thermally conductive sheets are melted and kneaded    again along with thermally conductive material pellets or the raw    materials of the present invention and formed into a sheet to    produce a thermally conductive sheet.

The content of the collected thermally conductive sheets is preferably100 mass % or less, more preferably 50 mass % or less, and much morepreferably 30 mass % or less based on 100 mass % of the collectedthermally conductive sheets plus the thermally conductive material orthe raw materials of the present invention. Such a range allows for therecycling of the thermally conductive material and the thermallyconductive sheet molded from the thermally conductive material whilemaintaining the characteristics of the thermally conductive material andthe thermally conductive sheet molded therefrom.

The thermally conductive material according to the present invention andthe thermally conductive sheet molded therefrom are preferably used inapplications that require high thermal conductivity, electricalinsulation, flexibility, toughness, and flame retardancy, such asThermally conductive parts for computers: personal computers, video gamemachines and the like, and cell phones and the like;

-   Thermally conductive parts for display power supply units and the    like: home televisions, plasma displays, liquid crystal televisions,    and the like;-   Thermally conductive parts for AV equipment, OA equipment, and the    like: DVD players, DVD recorders, HDD recorders, home televisions,    plasma displays, liquid crystal televisions, and the like;-   Thermally conductive parts for light sources for LED backlight:    liquid crystal TVs and the like;-   Thermally conductive parts for automobile electric/electronic    members: car stereos, car navigation systems, and the like; and-   Other thermally conductive parts: inverters, lights, air    conditioners, and the like.

The content of the vinyl aromatic unit and the content of the polymerblock comprising a vinyl aromatic were determined with unhydrogenatedcopolymers because their values before and after hydrogenation remainedunchanged under the hydrogenation conditions of the present invention.

Here, to determine the content of each raw material and the compositionfrom the states of the thermally conductive material and the thermallyconductive sheet, the thermally conductive material or the thermallyconductive sheet is dissolved in chloroform, cyclohexane, acyclohexane-chloroform solvent mixture mixed at an appropriate ratio orthe like and the resulting solution is used for the determination.

In addition, when the vinyl aromatic polymer block content is calculatedfrom a hydrogenated copolymer, a nuclear magnetic resonance (NMR)apparatus (JMN-270WB, JEOL Ltd.) is used and the method described in Y.Tanaka, et al., Rubber Chemistry and Technology 54, 685(1981) isfollowed. Specifically, 30 mg of a hydrogenated copolymer is dissolvedin 1 g of deuterated chloroform to prepare a sample and measure the¹H-NMR spectrum of the sample. If the vinyl aromatic is styrene, theapparent vinyl aromatic polymer block content (Ns) obtained by NMRmeasurement and the vinyl aromatic polymer block content (Os) arecalculated with the following numbers and the following formulas.Block styrene strength (S1)=(value integrated from 6.9 to 6.3 ppm)/²Random styrene strength (S2)=(value integrated from 7.5 to 6.9ppm)−3×(S1)Ethylene-butylene strength (EB)=Total integrated value−3×[(S1)+(S2)]/8Apparent vinyl aromatic polymer block content(Ns)=104×(S1)/[104×{(S1)+(S2)}+56×(EB)]Os=−0.012×(NS)²+1.8×(Ns)−13.0

EXAMPLES

The present invention will be specifically described below withExamples, and the present invention is not limited only to the Examples.

[Raw Materials]

<Hydrogenated Copolymer (1)>

(Polymer 1)

This was produced by the following polymerization process.

Reaction Conditions and the Like

-   Reactor: A stirrer having an internal volume of 10 L and a jacketed    tank reactor-   Reaction temperature: Kept at 70° C. during polymerization.-   Kept at 65° C. during hydrogenation reaction.-   Hydrogenation catalyst: 1 L of dried and purified cyclohexane was    placed in a reaction vessel for nitrogen-substituted hydrogenation    catalyst preparation, to which 100 mmol of    bis(η5-cyclopentadienyl)titanium dichloride was then added. An    n-hexane solution containing 200 mmol of trimethylaluminum was    further added under vigorous stirring and reaction was allowed to    take place at room temperature for about 3 days to prepare the    desired catalyst.    Reaction Procedure-   (i) 10 mass parts of cyclohexane was placed in the reactor and    adjusted to a temperature of 70° C.-   (ii) As the first-stage reaction, 0.076 mass parts of n-butyllithium    and 0.4 mol of N,N,N′,N′-tetramethylethylenediamine (hereinafter    referred to as TMEDA) based on 1 mol of n-butyllithium were added.-   (iii) A cyclohexane solution (monomer concentration, 22 mass %)    containing 8 mass parts of styrene was added over about 3 minutes    and after completion of addition, reaction was allowed to take place    for 30 minutes.-   (iv) As the second-stage reaction, a cyclohexane solution (monomer    concentration, 22 mass %) containing 48 mass parts of 1,3-butadiene    and 36 mass parts of styrene was continuously fed to the reactor    over 60 minutes at a constant rate and after completion of addition,    reaction was allowed to take place for 30 minutes.-   (v) As the third-stage reaction, a cyclohexane solution (monomer    concentration, 22 mass %) containing 8 mass parts of styrene was    added over about 3 minutes and after completion of addition,    reaction was allowed to take place for 30 minutes to obtain a    copolymer.-   (vi) 100 mass ppm of the hydrogenation catalyst in terms of the    amount of titanium was added to the copolymer obtained, and    hydrogenation reaction was allowed to take place at a hydrogen    pressure of 0.7 MPa and a temperature of 65° C.-   (vii) After completion of reduction, methanol was added and then 0.3    mass % of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate was    added as a stabilizer based 100 mass % of the copolymer to obtain a    hydrogenated copolymer.

The hydrogenated copolymer obtained had a weight-average molecularweight of 16.5×10⁴, a molecular weight distribution of 1.2, and a degreeof hydrogenation of 99%. In addition, dynamic viscoelasticitymeasurement showed that the peak temperature of tan δ was at −15° C.Moreover, DSC measurement showed no crystallization peak.

In addition, the content of the vinyl aromatic unit calculated from theunhydrogenated copolymer obtained after the third-stage reaction was 52mass %, the content of the polymer block comprising a vinyl aromatic was16 mass %, and the vinyl bond content of the 1,3-butadiene part was 21mass %.

(Polymer 2)

This was produced by the following polymerization process.

An unhydrogenated copolymer was obtained in the same way as polymer 1except for the use of 4.5 mass parts of styrene at the first stage, 49mass parts of 1,3-butadiene and 42 mass parts of styrene at the secondstage, and 4.5 mass part of styrene at the third stage. Next,hydrogenation reaction was allowed to take place as with polymer 1 toobtain a hydrogenated copolymer. The hydrogenated copolymer obtained hasa weight-average molecular weight of 17.5×10⁴, a molecular weightdistribution of 1.2, and a degree of hydrogenation of 99%. In addition,dynamic viscoelasticity measurement showed that the peak temperature oftan δ was at −14° C. Moreover, DSC measurement showed no crystallizationpeak.

In addition, the content of the vinyl aromatic unit calculated from theunhydrogenated copolymer obtained after the third-stage reaction was 51mass %, the content of the polymer block comprising a vinyl aromatic was9 mass %, the vinyl bond content of the butadiene part was 21 mass %.

<Modified Hydrogenated Copolymer (2)>

(Polymer 3)

This was produced by the following polymerization process.

A modified copolymer was obtained in the same way as polymer 1 exceptthat as the third-stage reaction in producing polymer 1, the same moleof styrene and the modifier tetraglycidyl-1,3-bisaminomethylcyclohexaneas the mole of n-butyllithium was added to the living polymer solutionobtained at the second-stage reaction and reaction was allowed to takeplace. The modified copolymer obtained had a weight-average molecularweight of 16.5×10⁴, a molecular weight distribution of 1.2, a degree ofhydrogenation of 99%, and a degree of modification of 80%. In addition,dynamic viscoelasticity measurement showed that the peak temperature oftans was at −15° C. Moreover, DSC measurement showed no crystallizationpeak.

In addition, the content of the vinyl aromatic unit calculated from theunhydrogenated modified copolymer obtained after the third-stagereaction was 52 mass %, the content of the polymer block comprising avinyl aromatic was 16 mass %, and the vinyl bond content of thebutadiene part was 21 mass %.

<Other Thermoplastic Resins>

(Polymer 4)

Tuftec (registered trademark) H1043 (styrene/ethylene-butylene=67/33), ahydrogenated styrene thermoplastic elastomer (SEBS), from Asahi KaseiChemicals Corporation

(Polymer 5)

SunAllomer (trade name) PM900A, a polypropylene resin, from SunAllomerLtd.

<Zinc Oxide (3)>

[Zinc Oxide A]

Pana-Tetra (registered trademark) WZ-0501, having a core part andacicular crystal parts extending from the core part in four differentaxial directions, (no surface treatment; the diameter of the base of theacicular crystal parts, 0.7 to 14 μm; the length from the base of theacicular crystal parts and an end, 3 to 200 μm), from AMTEC Co., Ltd.

[Zinc Oxide B]

Ginrei (registered trademark) A, having a spherical structure (averageparticle size, 0.2 μm), from Toho Zinc Co., Ltd.

<Paraffin Oil (4)>

Diana (registered trademark) Process Oil PW380] (kinematic viscosity at40° C., 382 mm²/s) from Idemitsu Kosan Co., Ltd.

<Flame Retardant (5)>

[Flame Retardant A]

Firecut (trade name) P-680 (bis(dibromopropyl)tetrabromobisphenol A(DBP-TBBA)), a halogen-based flame retardant, from Suzuhiro ChemicalCo., Ltd.

[Flame Retardant B]

Pyroguard (registered trademark) AN-800(T) (antimony trioxide) fromDai-ichi Kogyo Seiyaku Co., Ltd.

[Flame Retardant C]

SPS-100 (trade name) (phenoxyphosphazene; n=3, 90 mass % or more), aphosphorus-based flame retardant, from Otsuka Chemical Co., Ltd.

[Flame Retardant D]

Pyrolyzer (registered trademark) HG, a nonhalogen, nonphosphorus flameretardant, (aluminum hydroxide surface-treated with ammonium nitrate;average particle size, 1.1 μm), from Ishizuka Glass Co., Ltd.

[Flame Retardant E]

Metablen (registered trademark) A-3800J, a polytetrafluoroethylene, fromMitsubishi Rayon Co., Ltd.

<Filler (6)>

[Filler A]

SHOBN (registered trademark) UHP-1, a boron nitride, (average particlesize, 10 μm; thermal conductivity, about 130 W/m·K), from Showa DenkoK.K.

[Filler B]

SN-EO3 (trade name), a high-purity silicon nitride powder, (averageparticle size, 1.0 μm; thermal conductivity, about 80 W/m·K), from UbeIndustries, Ltd.

[Filler C]

Shapal E-Grade (registered trademark), a high-purity aluminum nitridepowder, (average particle size, 1.1 μm; thermal conductivity, about 200W/m·K), from Tokuyama Corporation.

[Filler D]

Spherical graphite SG-BL40 (trade name), having a spherical structure,(average particle size, 40 μm), from Ito Kokuen Co., Ltd.

[Filler E]

SYZR3252 (trade name), an expanded graphite, (average particle size, 45μm), from Sanyo Trading Co., Ltd. Expanded graphite has aflame-retardant effect.

<Additives>

[Additive A]

Adeka (registered trademark) Fatty Acid SA-200 (stearic acid) from AdekaCorporation.

[Additive B]

Hiblen (trade name) B403, an acrylic resin, from Zeon KASEI Co., Ltd.

[Processes for Fabricating Samples]

The fabricated samples evaluated in Examples 1 to 22 and ComparativeExamples 1 to 9 were fabricated by using the following processes.

(Press-Molded Sheet)

A thermally conductive material pellet was kneaded with a 3-inch rollkneader at 200° C. and formed into a sheet. This sheet was thensubjected to press molding involving heating at 200° C. to obtain a 120mm long×220 mm wide, 1 mm-thick press-molded sheet. Similarly, 2mm-thick and 5 mm-thick press-molded sheets were also prepared.

(0.3 mm-Thick Formed T-Die Sheet)

A single-screw extruder set at 190° C. (Toyo Seiki Seisaku-sho, Ltd.;Labo Plastomill model, SOM; Screw model, D2020) and a 120 mm-wide T-die(Toyo Seiki Seisaku-sho, Ltd.) with the thickness of the T-die lipadjusted to 0.3 mm was used to obtain an about 100 mm-wide, 0.3 mm-thickformed T-die sheet from a thermally conductive material pellet.

The fabricated samples evaluated in Examples 19 and 20 were fabricatedby using the following processes.

(Calendering)

Raw materials having the composition of Example 2 were melted andkneaded for 5 minutes with a pressure kneader set at a volume of 75 L, atemperature of 170° C., and a blade rotational speed of 20 rpm to obtaina mass of a thermally conductive material. The mass of a thermallyconductive material was formed into a 200 mm-wide, 10 mm-thick sheet byusing a counter-rotating twin-screw extruder with a die installed at thetip of the extruder at a cylinder temperature of 150° C. The sheet wascalendered by using a roll calendering machine with the calender rolldiameter adjusted to 1000 mm, the width to 1600 mm, the temperature to140° C., and the roll gap to 1 mm to obtain an about 1000 mm-wide, 1mm-thick sheet.

(T-Die Sheet Forming)

The thermally conductive material pellet obtained in Example 2 wasformed into a 1 mm-thick sheet by using a single-screw extruder set at190° C. (Toyo Seiki Seisaku-sho, Ltd.; Labo Plastomill model, 50M; Screwmodel, D2020) and a 120 mm-wide T-die (Toyo Seiki Seisaku-sho, Ltd.)with the thickness of the T-die lip adjusted to 1 mm and the take-offspeed adjusted (Toyo Seiki Seisaku-sho, Ltd.; conveyor-type take-offsystem, Conveyor CON type).

[Measurement of Physical Characteristics]

1) Content of a Vinyl Aromatic Unit

-   Measurement instrument: Ultraviolet spectrophotometer (UV-2450,    Shimadzu Corporation)-   Sample: 50 mg of an unhydrogenated copolymer dissolved in 100 mL of    chloroform-   Measurement wavelength: 254 nm-   Calibration curve: The absolute calibration curve was prepared by    varying the styrene concentration of a styrene/chloroform solution.    2) Content of a Polymer Block Comprising a Vinyl Aromatic

An unhydrogenated copolymer was used to measure the content by theosmium tetraoxide degradation method described in I.M. Kolthohoff, etal., J. Polym. Sci. 1,429(1946). To degrade the unhydrogenatedcopolymer, 0.1 g of osmic acid in 125 mL of a tertiary butanol solutionwas used.

3) Vinyl Bond Content Based on the Conjugated Diene

-   Measurement instrument: Infrared spectrophotometer (FT/IR-230,    Hitachi, Ltd.)-   Sample: 50 mg of a hydrogenated copolymer or a modified hydrogenated    copolymer dissolved in 10 cc of carbon bisulfide-   Measurement method: The above solution was put in a 1 mm-thick KBr    liquid cell to measure transmittances at 960 cm⁻¹ (trans), 910 cm⁻¹    (vinyl), 724 cm⁻¹ (cis), and 699 cm⁻¹ (styrene) and calculate the    content from the measurements by the Hampton technique    4) Degree of Hydrogenation-   Measurement instrument: Nuclear magnetic resonance apparatus    (JNM-LA400, JEOL Ltd.)-   Sample: Deuterated chloroform solution of a 5 wt % hydrogenated    copolymer or modified copolymer-   Observation frequency: 400 MHz-   Chemical shift reference: TMS-   Pulse delay: 2.9 s-   Number of scans: 128-   Pulse width: 45°-   Measurement temperature: 23° C.

¹H-NMR measurement was performed under the above conditions to calculatethe degree of hydrogenation from styrene units (0 to 8 ppm),1,4-butadiene (4.5 to 4.8 ppm), 1,2-butadiene units (4.9 to 5.7 ppm).

5) Weight-Average Molecular Weight and Molecular Weight Distribution

-   Measurement instrument: GPC (LC-10, Shimadzu Corporation) Column:    Set of 4 columns connected in series consisting of one Shim-pac 803,    two 804, and one 805, Shimadzu Corporation-   Detector: RI (differential refractometry) detector-   Sample: 10 mg of a hydrogenated copolymer or a modified hydrogenated    copolymer dissolved in 20 cc of tetrahydrofuran-   Developing solvent: tetrahydrofuran; flow rate, 1 mL/min-   Measurement temperature: 40° C.-   Calibration curve reference sample: TSK Standard-   Polystyrene (Mw/Mn<1.2, 10²<Mw≦10⁸, 8 types), Tosoh Corporation; a    tetrahydrofuran solution having the same concentration of that of    the sample was prepared.

Note that the molecular weight when there are multiple peaks on achromatogram refers to the average molecular weight calculated from themolecular weight corresponding to each peak and the composition ratio ofthe peaks (as determined from the area ratio at each peak on thechromatogram). In addition, the molecular weight distribution is a ratioof the weight-average molecular weight obtained to the number-averagemolecular weight obtained.

6) Crystallization Peak and the Amount of Heat Required forCrystallization at the Peak

-   Measurement instrument: Differential scanning calorimeter (DSC)    (DSC3200S, Mac Science Co., Ltd.)-   Temperature rise conditions:-   Step 1: Temperature was raised from room temperature to 150° C. at a    rate of temperature rise of 30° C./min-   Step 2: Temperature was lowered to −100° C. at a rate of temperature    drop of 10° C./min

A crystallization curve was prepared to check for any crystallizationpeak. When a crystallization peak was found, the temperature at whichthe peak appeared was defined as the crystallization peak temperature.The amount of heat required for crystallization at the peak wascalculated from its peak area.

7) Degree of Modification

A modified copolymer was adsorbed on a GPC column that uses a silica gelas a filler, but not on a GPC column that uses a polystyrene gel as afiller. These characteristics were used to calculate the degree ofmodification.

-   Measurement instrument: GPC (LC-10, Shimadzu Corporation)    Column:-   1) Polystyrene gel column: Set of 4 columns connected in series    consisting of 1×Shim-pac 803, 2×804, and 1×805, Shimadzu Corporation-   2) Silica gel column: Set of 3 columns connected in series    consisting of 1×Zorbax PSM60S and 2×PSM300S, DuPont-   Detector: RI (differential refractometry) detector-   Sample: 10 mg of a hydrogenated copolymer or a modified hydrogenated    copolymer dissolved in 20 cc of tetrahydrofuran-   Developing solvent: Tetrahydrofuran; flow rate, 1 mL/min Measurement    temperature: 40° C.-   Calibration curve reference sample: TSK Standard Polystyrene    (Mw/Mn<1.2, 10²<Mw≦10⁸, 8 types), Tosoh Corporation; a    tetrahydrofuran solution having the same concentration of that of    the sample.

The above polystyrene gel column and silica gel column were used toproduce the chromatogram for each of the two samples. The amount ofadsorption on the silical gel column was calculated from the differencebetween these peak areas to find the degree of modification.

8) Loss Tangent (tan δ)

-   Measurement instrument: Dynamic viscoelastic analyzer (DVE-V4,    Rheology K.K.)-   Rate of temperature rise: 1° C./min-   Measurement mode: Shear mode-   Measurement frequency: 10 MHz-   Evaluation sample: 1 mm-thick press-molded sheet

The viscoelastic spectrum was measured under the above conditions tocalculate the peak temperature of tan δ.

[Method of Evaluating Physical Characteristics]

1) Sample for Thermal Conductivity Evaluation: 0.3 mm-Thick T-Die MoldedSheet

-   Evaluation device: Quick Thermal Conductivity Meter (QTM-500, Kyoto    Electronics Manufacturing Co., Ltd.)-   Measurement technique: Hot-wire method-   Software used: Software for measuring thermal conductivity of thin    sheet (SOFT-QTM5W, Kyoto Electronics Manufacturing Co., Ltd.)-   Measurement method: The method described in Japanese Patent    Publication No. 5-12361 in which measurement was performed with a    reference plate whose thermal conductivity was known (foamed    polyethylene, silicon rubber, quartz glass, mullite, or zirconia) to    determine the thermal conductivity with a box-type probe (model No.    PD-11) was used.    2) Electrical Insulation-   Evaluation sample: 0.3 mm-thick T-die molded sheet-   Evaluation instrument: Super-megohmmeter (model No. SM-8220, Toa    Dempa Kogyo K.K.)-   Measurement electrode: Electrode for plate samples (model No.    SME-8311, Toa Dempa Kogyo K.K.)-   Measurement method: After a voltage of 100 V was applied to a    thermally conductive sheet measuring 10 cm per side formed from a    thermally conductive material for 50 seconds, the volume resistance    (Rv) after 10 seconds was measured to calculate the volume    resistivity from the following formula.    Volume resistivity (Ω·cm)=30/(sheet thickness [mm])−Rv-   The volume resistivities for 5 different locations were    arithmetically averaged to calculate the volume resistivity (Ω·cm)    3) Hardness-   Evaluation sample: 1 mm-thick press-molded sheet Evaluation    instrument: Durometer Type A, Shimadzu Corporation; JIS A durometer-   Measurement method: Measurement after 10 seconds according to JIS    K6253    4) Toughness    <Toughness 1>-   Evaluation sample: a 1 mm-thick press-molded sheet folded in half    (after holding in half, 120 mm long×about 110 mm wide)

2 kg of a weight was put on the evaluation sample (pressure, about 15g/cm²) which was then left to stand at room temperature for 24 hours toevaluate whether or not there is fold cracking.

Evaluation Criteria:

-   Absence of fold cracking: ◯-   Presence of fold cracking: Δ-   Inability to fold in half (poor flexibility): ×    <Toughness 2>-   Evaluation sample: 0.3 mm-thick T-die molded sheet Test speed: 200    mm/min-   The tear strength was measured by following the JIS K7128-3 angle    tear test procedure.    Evaluation Criteria:-   Tear strength of 30 N/mm or more: ◯-   Tear strength of 10 N/mm or more and less than 30 N/mm: Δ-   Tear strength of less than 10 N/mm: ×    5) Flame Retardancy-   Evaluation sample: A sheet 127 mm long×12.7 mm wide×1 mm thick    prepared from a 1 mm-thick press-molded sheet

According to the UL-94 (standards established by U.S. Underwriters'Laboratories Inc.) vertical burning test, a flame was placed under thesample for 10 seconds and then removed, and the time taken for thesample to stop burning was measured. After the sample stopped burning,the flame was placed again under the sample for a further 10 seconds andthen removed, and the time taken for the sample to stop burning wasmeasured. A pair of 5 samples was evaluated (the burning time wasmeasured a total of 10 times). The maximum burning time of 10 burningtimes, the total of 10 burning times, and whether or not there are dripsduring burning were evaluated.

The ratings for flame retardancy classification are given below. Theother details are according to the UL-94 standards.

-   V-0: Maximum burning time, 10 seconds or less; total burning time,    50 seconds or less; no drips-   V-1: Maximum burning time, 30 seconds or less; total burning time,    250 seconds or less; no drips-   V-2: Maximum burning time, 30 seconds or less; total burning time,    250 seconds or less; drips permitted-   Burning: The above conditions not satisfied    6) Chip Occurrence

The take-off speed of a pelletizer was adjusted so that the diameter ofa strand extruded from an extruder was 2 to 3 mm (both inclusive) duringproducing a thermally conductive material pellet. The chip occurrence ofthe pellet obtained was calculated from the following formula.Chip occurrence (mass %)=[(W1−W2)/W1]×100

-   W1: About 100 g of the pelletized pellet precisely weighed-   W2: The amount of pellet precisely weighed remaining on a 60-mesh    metal screen with which chips were separated from the pellet after    W1 was precisely weighed    Evaluation Criteria:-   Amount of chips occurring, less than 0.1 mass %: ♦-   Amount of chips occurring, 0.1 mass % or more and less than 0.3 mass    %: ◯-   Amount of chips occurring, 0.3 mass % or more and less than 0.6 mass    %: Δ-   Amount of chips occurring, 0.6 mass % or more: ×

Examples 1 to 18 and Comparative Examples 1 to 9

Components added at their compositions shown in Tables 1 and 2 weremelted and kneaded with a twin-screw extruder set at a cylindertemperature of 200° C. and a screw rotational speed of 200 rpm (ZSK-25;25 mm φ; L/D=52; entire length of the heating part, 1300 mm; Werner &Pfleiderer Industrielle Backtechnik GmbH) to obtain a thermallyconductive material pellet.

However, in Comparative Example 3, the paraffin oil (4) bled out, andthis prevented the planned composition from being obtained, whereas inComparative Examples 4 and 8, no uniform composition was obtained.

Examples 19 and 20

In Example 19, 1 mm-thick resin sheet was obtained with the compositionof Example 2 by calendering.

In Example 20, a thermally conductive sheet specimen formed from a 1mm-thick thermally conductive material was obtained with the compositionof Example 2 by T-die sheet forming.

Table 3 shows results of evaluation comparing the formed products withthe 1 mm-thick press-formed sheet of Example 2.

Examples 21 and 22

In Example 21, a 2 mm-thick resin sheet was obtained and in Example 22,a 5 mm-thick resin sheet was obtained with the composition of Example 9by press molding. Table 4 shows results of evaluation comparing thesemolded products with the 1 mm-thick press-molded sheet of Example 9.

INDUSTRIAL APPLICABILITY

The thermally conductive material according to the present invention andthe thermally conductive sheet molded therefrom are preferably used inapplications that require high thermal conductivity, electricalinsulation, flexibility, toughness, and flame retardancy, such as

-   Thermally conductive parts for computers: Personal computers, video    game machines and the like, and cell phones and the like;-   Thermally conductive parts for display power supply units and the    like: Home televisions, plasma displays, liquid crystal televisions,    and the like;-   Thermally conductive parts for AV equipment, OA equipment, and the    like: DVD players, DVD recorders, HDD recorders, home televisions,    plasma displays, liquid crystal televisions, and the like;-   Thermally conductive parts for light sources for LED backlight:    Liquid crystal TVs and the like;-   Thermally conductive parts for automobile electric/electronic    members: Car stereos, car navigation systems, and the like;-   Other thermally conductive parts: Inverters, lights, air    conditioners, and the like.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Content Hydrogenated Polymer1 15 7.5 5 8.5 (mass %) copolymer (1) Polymer 2 7.5 Modified Polymer 37.5 5 hydrogenated copolymer (2) Other Polymer 4 thermoplastic Polymer 5resin Zinc oxide (3) Zinc oxide A 60 80 80 80 70 69 Zinc oxide BParaffin oil (4) Paraffin oil 15 7.5 7.5 7.5 10 8.5 Flame Flameretardant A 8 retardant (5) Flame retardant B 4 Flame retardant C 10 5 55 10 Flame retardant D Flame retardant E 2 Filler (6) Filler A Filler BFiller C Filler D Filler E Additive Additive A 0.2 0.2 0.2 0.2 0.1 0.1Additive B 0.2 0.2 0.2 0.2 0.1 0.1 Physical Thermal conductivity (W/m ·K) 1.0 1.8 1.8 1.7 1.5 1.5 characteristics Volume resistivity (Ω · cm) 2× 10¹¹ 2 × 10¹⁰ 3 × 10¹⁰ 2 × 10¹⁰ 2 × 10¹¹ 1 × 10¹¹ evaluation Hardness(JIS A) 73 78 71 81 73 75 Chip occurrence ♦ ♦ ♦ ♦ ♦ ♦ Toughness 1 ◯ ◯ ◯◯ ◯ ◯ Toughness 2 ◯ ◯ ◯ ◯ ◯ ◯ Flame retardancy V-2 V-2 V-2 V-2 V-2 V-0Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Content Hydrogenated Polymer 18.5 10 17.5 10 20 6.9 (mass %) copolymer (1) Polymer 2 Modified Polymer3 hydrogenated copolymer (2) Other Polymer 4 thermoplastic Polymer 5resin Zinc oxide (3) Zinc oxide A 69.9 60 60 65 62.5 75.4 Zinc oxide BParaffin oil (4) Paraffin oil 8.5 10 17.5 15 7.5 6.9 Flame Flameretardant A 1.8 retardant (5) Flame retardant B 0.9 Flame retardant C 55 10 10 6 Flame retardant D 5 20 Flame retardant E 0.4 Filler (6) FillerA 4.8 Filler B Filler C Filler D Filler E Additive Additive A 0.1 0.10.2 0.1 0.1 0.9 Additive B 0.1 0.1 0.2 0.1 0.1 0.2 Physical Thermalconductivity (W/m · K) 1.6 1.2 1.0 1.5 1.2 2.1 characteristics Volumeresistivity (Ω · cm) 9 × 10¹⁰ 5 × 10¹¹ 2 × 10¹² 7 × 10¹¹ 2 × 10¹¹ 2 ×10¹² evaluation Hardness (JIS A) 77 71 42 62 49 86 Chip occurrence ♦ ♦ ♦♦ ♦ ◯ Toughness 1 ◯ ◯ ◯ ◯ ◯ ◯ Toughness 2 ◯ ◯ ◯ ◯ ◯ ◯ Flame retardancyV-0 V-2 V-2 V-2 V-2 V-2 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18Content Hydrogenated Polymer 1 7.2 6.9 10 8.5 20 20 (mass %) copolymer(1) Polymer 2 Modified Polymer 3 hydrogenated copolymer (2) OtherPolymer 4 thermoplastic Polymer 5 resin Zinc oxide (3) Zinc oxide A 7672.5 63 63.9 80 60 Zinc oxide B Paraffin oil (4) Paraffin oil 7.2 6.9 108.5 20 Flame Flame retardant A 1.8 retardant (5) Flame retardant B 0.9Flame retardant C 4.8 4.7 7 3 Flame retardant D 3 Flame retardant E 0.4Filler (6) Filler A Filler B 4.8 Filler C 9 Filler D 10 Filler E 10Additive Additive A 0.2 0.9 0.1 0.1 0.1 0.1 Additive B 0.2 0.2 0.1 0.10.1 0.1 Physical Thermal conductivity (W/m · K) 1.9 1.9 2.5 2.4 1.8 1characteristics Volume resistivity (Ω · cm) 6 × 10¹² 9 × 10¹³ 2 × 10⁸ 8× 10⁸ 1 × 10¹⁰ 4 × 10¹² evaluation Hardness (JIS A) 83 81 75 83 91 35Chip occurrence ◯ ◯ ◯ ◯ ♦ ♦ Toughness 1 ◯ ◯ ◯ ◯ ◯ ◯ Toughness 2 ◯ ◯ ◯ Δ◯ ◯ Flame retardancy V-2 V-2 V-2 V-0 Burning Burning

TABLE 2 Com. Com. Com. Com. Com. Com. Com. Com. Com. Ex. 1 Ex. 2 Ex. 3Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Content Hydrogenated Polymer 1 7.5 92.5 15 15 5 95 (mass %) copolymer (1) Polymer 2 Modified Polymer 3hydrogenated copolymer (2) Other Polymer 4 15 thermoplastic Polymer 5 30resin Zinc oxide (3) Zinc oxide A 60 41 91.5  5 67.5 40 95 5 Zinc oxideB 80 Paraffin oil (4) Paraffin oil 15 7.5 30 2.5 15 15 10 Flameretardant Flame (5) retardant A Flame retardant B Flame 10 5 20 3.5 20retardant C Flame 65 2.5 retardant D Flame retardant E Filler (6) FillerA Filler B Filler C Filler D Filler E Additive Additive A 0.2 0.2 0.20.2   0.1 0.1   0.1 0.1 0.1 Additive B 0.2 0.2 0.2 0.2   0.1 0.1   0.10.1 0.1 Physical Thermal conductivity 0.8 0.6 — —   0.3 1.8    0.35 —0.2 char- (W/m · K) acteristics Volume resistivity (Ω · cm) 1 × 10¹² 8 ×10¹¹ — — 8 × 10¹⁵ 5 × 10¹⁰ 6 × 10¹⁴ — 2 × 10¹⁶ evaluation Hardness (JISA) 85 78 — —   98< 66   98< — 66 Chip occurrence ♦ X — — X ♦ ♦ — ♦Toughness 1 Δ ◯ — — Δ ◯ Δ — ◯ Toughness 2 X ◯ — — X ◯ ◯ — ◯ Flameretardancy V-2 V-2 — — V-0 Burning V-2 — Burning

TABLE 3 Ex. 2 Ex. 19 Ex. 20 Method of producing resin sheet Pressmolding Calendering T-die sheet forming Physical Thermal conductivity(W/m · K) 1.8 2.0 1.6 characteristics Volume resistivity (Ω · cm) 2 ×10¹⁰ — — evaluation Hardness (JIS A) 78 69 77 Chip occurrence ♦ ♦ ♦Toughness 1 ◯ ◯ ◯ Toughness 2 ◯ ◯ ◯ Flame retardancy V-2 V-2 V-2

TABLE 4 Ex. 9 Ex. 21 Ex. 22 Method of producing resin sheet Pressmolding Press molding Press molding Sheet thickness (mm) 1 2 5 PhysicalThermal conductivity (W/m · K) 1.0 1.0 1.1 characteristics Volumeresistivity (Ω · cm) 2 × 10¹² 8 × 10¹² 9 × 10¹³ evaluation Hardness (JISA) 42 42 42 Chip occurrence ♦ ♦ ♦ Toughness 1 ◯ ◯ ◯ Toughness 2 ◯ ◯ ◯Flame retardancy V-2 V-2 V-1

The invention claimed is:
 1. A thermally conductive material comprising:a hydrogenated copolymer (1) satisfying the following conditions (a) to(d) which is produced by hydrogenating a copolymer of a conjugated dieneand a vinyl aromatic; and/or a modified hydrogenated copolymer (2)having at least one functional group and satisfying the followingconditions (a) to (d), which is produced by hydrogenating a copolymer ofa conjugated diene and a vinyl aromatic; a zinc oxide (3) comprising acore part and acicular crystal parts extending from the core in fourdifferent axial directions; and a paraffin oil (4), wherein thethermally conductive material does not comprise a flame retardant (5),and satisfies the following conditions (A) to (C): (a) the content of avinyl aromatic unit is greater than 45 mass % and 90 mass % or less, (b)the content of a vinyl aromatic polymer block is 40 mass % or less, (c)the weight-average molecular weight is 5×10⁴ to 100×10⁴, and (d) thedegree of hydrogenation of double bonds based on the conjugated diene is10% or more, and based on 100 mass % of the thermally conductivematerial, (A) the total content of the hydrogenated copolymer (1), themodified hydrogenated copolymer (2), and the paraffin oil (4),[(1)+(2)+(4)], is 10 mass % or more and 24 mass % or less, (B) thecontent of the zinc oxide (3) is 76 mass % or more and 90 mass % orless, and (C) the ratio of a mass of the paraffin oil (4) to the totalmass of the hydrogenated copolymer (1) and the modified hydrogenatedcopolymer (2), [(4)/{(1)+(2)}], is greater than 0 and 2 or less.
 2. Thethermally conductive material according to claim 1, wherein the modifiedhydrogenated copolymer (2) has at least one functional group selectedfrom a hydroxy group, an epoxy group, an amino group, a silanol group,and an alkoxysilane group.
 3. The thermally conductive materialaccording to claim 1, wherein the content of the vinyl aromatic polymerblock in the hydrogenated copolymer (1) and/or the modified hydrogenatedcopolymer (2) is 10 to 40 mass %.
 4. The thermally conductive materialaccording to claim 1, wherein the content of the vinyl aromatic polymerblock in the hydrogenated copolymer (1) and/or the modified hydrogenatedcopolymer (2) is less than 10 mass %.
 5. The thermally conductivematerial according to claim 1, wherein the hydrogenated copolymer (1)and/or the modified hydrogenated copolymer (2) has at least onestructure selected from the following general formulas:B;  (i)B-A;  (ii)B-A-B;  (iii)(B-A)_(m)-Z; and  (iv)(B-A)_(n)-Z-A_(p),  (v) (wherein B represents a random copolymer blockof the conjugated diene and the vinyl aromatic, and A represents thevinyl aromatic polymer block, m is an integer of 2 or more, and each ofn and p is an integer of 1 or more, Z represents a coupling agentresidue).
 6. The thermally conductive material according to claim 1,wherein the modified hydrogenated copolymer (2) has at least onefunctional group selected from the following formulas (a) to (n):

(wherein R1 to R4 independently represent hydrogen or a hydrocarbongroup having a carbon number of 1 to 24, or a hydrocarbon group having acarbon number of 1 to 24 which has a functional group selected from ahydroxy group, an epoxy group, an amino group, a silanol group, and analkoxysilane group, R5 represents a hydrocarbon chain having a carbonnumber of 1 to 48 or a hydrocarbon chain having a carbon number of 1 to48 which has a functional group selected from a hydroxy group, an epoxygroup, an amino group, a silanol group, and an alkoxysilane group,Elements such as oxygen, nitrogen, and silicon may bind to thehydrocarbon groups of R1 to R4 and the hydrocarbon chain of R5 in whicha binding way that such elements do not take a form of a hydroxy group,an epoxy group, a silanol group, or an alkoxysilane group, R6 representshydrogen or an alkyl group having a carbon number of 1 to 8).
 7. Thethermally conductive material according to claim 1, wherein the modifiedhydrogenated copolymer (2) is obtained by allowing addition reaction totake place between a modifier containing a functional group and a livingend of an unhydrogenated copolymer obtained with an organolithiumcompound as a polymerization catalyst and then hydrogenating themodified unhydrogenated copolymer (2) obtained.
 8. The thermallyconductive material according to claim 1, wherein the content of thezinc oxide (3) is 65 mass % or more and 90 mass % or less based on 100mass % of the thermally conductive material.
 9. A thermally conductivesheet having a thickness of 30 μm to 1 mm, which is obtained by moldingfrom the thermally conductive material claim
 1. 10. A thermallyconductive sheet having a thickness of greater than 1 mm to 3 cm orless, which is obtained by molding from the thermally conductivematerial of claim 1.